Two potholers, Davis and Spencer, make their way down a metal rope ladder into a cave with a remarkable amount of stalactites. They are delighted at the sight of its majesty, but a loud roar spooks both men and incites them to find out where it came from. As they continue down a tunnel, another roar bellows from the distance. When Davis rounds a corner, he is met with the hostile face of a reptilian creature. Davis is mauled to death. Spencer dashes over to find the body. He sees the creatures and runs away screaming.
In a UNIT garage, The Doctor is merrily working to restore a bright yellow vintage car, which he had been given at his request, humming the first lines of Jabberwocky. A license plate emblazoned “WHO 1” lies in front of him as he sits beneath the car’s undercarriage fixing its parts. Liz enters the room and calls for him. The Doctor doesn’t hear her and continues to tinker away at his vehicle, which he has affectionately nicknamed “Bessie”, telling it to cooperate when it becomes a hassle to repair its chassis. Liz approaches The Doctor directly and gets him to emerge from underneath Bessie. She is sceptical to think he can get it running, but The Doctor is quick to defend his car, stating it has great character and he was very lucky to get it. The Doctor plans to take it for a test drive, though he seems to have left out a metal hoop, at which he looks with confusion. Unable to recognise the part, he tosses it aside. Liz informs The Doctor that the Brigadier has an urgent message for the two of them w
hile he’s away investigating scientists. They are to go to Wenley Moor forthwith to attend a meeting. Seeing it as beneath him to comply, The Doctor claims he’s too busy, and goes back to work on Bessie. However, Liz tries to make it sound like less of an order by noting that Wenley Moor is famous for its caves. Eager to give Bessie a trial run, he submits. The Doctor kisses his hand and plants it on Bessie’s radiator. Her engine starts, and the car rumbles to life.
At the moor, the director, Charles Lawrence, is speaking about the issues regarding their facilities. He resents UNIT’s presence and feels it will interfere with the working of the plant. A UNIT soldier enters and notifies Lethbridge-Stewart that The Doctor and Liz Shaw have arrived, and he leaves to meet them. The Doctor isn’t pleased to be called in for a simple meeting but follows the Brigadier and Liz back to the conference room with the hope it is important. Shortly after the trio enters the conference room, Lawrence concludes the meeting. The Brigadier introduces his colleagues to Lawrence, Doctor Quinn, his number two, and Major Baker, station security officer. The group tells the trio they are at an experimental nuclear power research centre for a cyclotron: a proton accelerator. They are trying a new process to convert nuclear energy directly into electric power. It is experiencing mysterious power drains and a high incidence of mental breakdowns, absenteeism, and accidents. This has stagnated their research program, and Lawrence refuses to let it continue. UNIT have been called in to investigate. Brigadierorders Baker to triple check security arrangements and puts Liz in charge of investigating the issues with the personnel, and the Doctor is given charge of the scientific troubles. The Brigadier establishes the conference room as his working HQ so Lawrence will not complain that UNIT is interfering with the operation of the centre. After everyone but Baker and the Brigadier have left the room, Baker confides to him that he believes there is a saboteur working from the inside.
Quinn shows The Doctor and Liz the heart of the cyclotron. The Doctor is bemused to learn it is still being tested while power failures are happening. If one occurred at a critical time, when the machine was in use, it could incite a massive atomic explosion equal to a nuclear bomb. Quinn replies it is up to Lawrence to shut down the cyclotron, whom The Doctor knows is being too stubborn to halt the research. Suddenly, Liz becomes dizzy and grips her forehead. The Doctor sees Liz in pain and voices concern. She says she is okay, then departs to examine her reports of personnel. Quinn assumes his duties at a booth while The Doctor commends the scientists for constructing an underground accelerator. Quinn expresses his like of potholing to The Doctor because the caves intrigue him, but he isn’t so keen anymore, as recently one of the workers at the centre was killed while exploring the caves with a companion on their day off. He says they have brought in Doctor Meredith from a local hospital to treat the survivor, Spencer, who is still in the sick bay. Quinn feels the status of his condition and what happened to him are being covered up. The Doctor grows suspicious. He asks if the power losses follow a pattern. When Quinn says the scientists think of them as random, The Doctor requests to look at the reports. Quinn hands over the log showing the power losses, and the Doctor notices the log is incomplete. Quinn summons Miss Dawson and asks who was responsible for maintaining the log. She states it was Spencer, the same man who has been kept in the sick bay, leaving no one to update it. Despite this explanation, The Doctor finds it more complicated than the log falling out of date — he’s discovered some pages have been torn out entirely. Quinn and Dawson exchange troubled looks.
In the medical wing, Liz speaks to Doctor Meredith about the recent outbreak of mentally-affected patients. He does not understand why UNIT have been called in. They are soon joined by The Doctor, who wishes to see Spencer, but Meredith won’t allow it; Spencer is due to be moved to the local hospital, and the Doctor has no authority to warrant a visit. The Doctor briskly asserts his power as an associate of UNIT. Meredith concedes but warns him the visit is at his own risk.
The group enters the sick bay to find Spencer scribbling with a markeron the walls. A member of the medical staff is supervising him, who walks out to allow Meredith to take over. Spencer has emerged from a coma and has previously tried to throttle Meredith when he tried to administer treatment. He’s left Spencer to mark up the room’s walls, since it’s all that keeps him quiet. The Doctor approaches him to see if he can communicate as Liz warns him to be careful. He tries to speak to Spencer, but the man jumps and panics, immediately wresting his hands around The Doctor’s throat and forcing him down onto a cot. Liz and Meredith rush to subdue him, but The Doctor tells them to stop and pries Spencer’s hands loose and quells his violent reaction. Spencer resumes his scribbling while The Doctor nurses his neck. He remarks that a great fear has caused his mind to regress millions of years.
Off in a cornerof the cyclotron testing room, Quinn argues with Miss Dawson when she protests that they should stop “them” from taking the power. Dawson pleads with Quinn to order “them” to stop. He says he has already tried, and they have refused to listen. She implores him to tell Bakeror the Brigadier, but he refuses. When she warns him of the risk, he states that the promise of potential knowledge gain has outweighed the risk.
The Brigadier and Baker discuss UNIT’s security clearance while the Brigadier checks the security reports. Baker says he has no central intelligence records of the Doctor, but the Brigadier states The Doctor is his responsibility. The Doctor returns to the conference room, and the Brigadier excuses Baker, giving him a chance to warn The Doctor he’s trying to run a security check.
Lawrence checks on Quinn before the next test. Quinn states that all is normal. Quinn asks to run some supplementary tests, but Lawrence blocks it as they are already behind schedule. The experiment begins. One of the scientists, Roberts, seems in a daze.
The Doctor has explained his discoveries to the Brigadier, but the Brigadier is sceptical of any link. They are interrupted by a power failure.
The Doctor charges into the cyclotron testing chamber and learns it is undergoing a dangerous fluctuation in power. As the operators attempt to stabilise the nuclear reactions, they shut down two sectors. Roberts is due to close down the third sector, but suddenly he goes completely still. Dawson tries to get his attention, but he attacks her. The Doctor and the Brigadier grab hold of him and rescue Dawson, the Brigadier knocking Roberts out. The Doctor manages to stabilise sector three.
The Doctor returns to Liz to check the medical patients’ records. There has been a startling outbreak of neuroses in the cyclotron room, where she previously felt ill. She describes how she felt as oppression and horror. The Doctor thinks it doesn’t have anything to do with the cyclotron itself, but the caves. That room is deepest and closest to the cave systems. He also believes the sickness affects only some people. The two look at the reports of Davis’s death. His death was caused by a fracture to his cranium, but unusual abrasions were found on his side that resembled scratches or claw marks.
Now changed into suitable clothes for exploration, The Doctor makes his way into the caves, where he hears a loud roar and goes to investigate. He finds a cave hammer and a rope abandoned from the last expedition. He hears the roar again, only closer, and draws nearer to the sound until he is in the same place as the original attack. He almost leaves, but hears the roar directly behind him. He turns to see a dinosaur, and it instantly bears down on him.
A beeping sound calls the creature off. The Doctor pursues the creature and finds a huge footprint embedded in the mud.
Liz has told the Brigadier about where The Doctor is. The Brigadier is angry that he has put himself into danger and that Liz let him. Baker has organised a search party and comes in with climbing equipment. The Brigadier apologises to Baker but is cut off when The Doctor enters.
Lawrence is questioning Quinn as to why the power supply is still failing. Lawrence tells Quinn of the Doctor’s disappearance in the caves. Quinn seems worried until he is told that he has been found and no search party will be deployed.
The Brigadier does not believe The Doctor has seen a dinosaur. Baker speculates that whoever has been draining the power may have mocked something up to scare people away. It is decided that they will all go and explore. The Doctor is bemused when the Brigadier and Baker talk about how to arm themselves.
The Doctor leads the way in the cave system. He seems confused when the footprint in the mud has gone. They hear a rumbling, and Baker runs off with the UNIT officer Captain Hawkins and two troops in pursuit. Baker sees a figure further down in the cave system. The figure raises its hand. Baker shoots above the figure’s head, but the bullet ricochets down and strikes it. The dinosaur then appears and attacks Baker. Hearing the screams, the rest of the party run to his aid and find Barker conscious but confused. Hawkins finds blood on the floor. Hawkins, the Brigadier and most of the other soldiers decide to follow the trail, leaving The Doctor and Morton to carry Baker back. The Doctor takes a sample of the blood, planning to take it to HQ for testing.
A wounded reptile creature emerges into the moorland.
The Doctor has discovered that the blood sample has many similarities with the blood of reptiles. The Brigadier enters, saying he has lost track of the creature and plans to summon more men and continue the search the following day. The Doctor lies and says that the results on the blood have proved inconclusive. The Brigadier tells everyone that Baker is alright and has a minor concussion. The Doctor wonders why the creature killed its first victim but was called off from himself and Baker. The Doctor theorises that there are two types of creature: one large and ferocious, the other small, more intelligent and less hostile.
The wounded creature stumbles into a barn.
Lawrence is furious with Miss Dawson when she tells him that Quinn has disappeared. Lawrence accuses him of being more interested in the book that he is writing than the project. The Doctor enters and is keen to question Quinn too.
Quinn is in the cave system. He reaches a certain point, and a door in the cave opens for him. He is led, in a trance, to a console. When he comes to his senses, he warns the creature he is talking to through a computer system of the UNIT soldiers. He is told that it is too late and that one of their men have injured one of their kind. Quinn says that the UNIT soldiers will withdraw if they stop taking the power. The creature refuses. The creature says Quinn must get their injured number back, but Quinn refuses. He is told that they will not share their scientific secrets with him unless he does. He relents. He is given a summoning device, put back in a trance and sent off.
The next morning a farmer named Squire discovers the creature in his barn. He calls for his wife, Doris, to call the police. The creature wakes up and attacks the farmer. Doris sees the creature and screams.
The UNIT soldiers have arrived and are to start to search for the creature in the moors. Lawrence enters and coldly tells the Brigadier that his men are not helping at all. The Doctor enters and says that he has investigated all the machinery and there is nothing wrong. The power is being affected by an outside agent. The Doctor recommends the closing of the base. Lawrence refuses and says he is going to go over the Brigadier’s head to get him to leave the site. Lawrence leaves, and the Brigadier gets a phone call informing him of Squire’s death. The police have noticed claw marks on his body.
Later The Doctor, the Brigadier and Liz are investigating the farmer’s body. He suspects that the farmer cornered the creature, causing it to attack. He observes that the claw marks are smaller than the ones on Baker. They are also not the main cause of death. Squire died of heart failure — of fear. The Doctor and the Brigadier are to interview Doris Squire, who has been hospitalised with shock, whilst Liz is to stay and carry out some forensic tests.
Doris is beside herself with shock. The Doctor draws a picture of a creature and shows it to Doris. Doris states this is what killed her husband, and the Doctor asks where the creature is. She responds, “In the barn.” The Doctor and the Brigadier realise the creature is still there.
Liz is doing her tests whilst the creature approaches her. She turns to see the creature just as it claws her across her face.
The creature attempts to leave, but is blocked by a policeman and turns back.
Dawson comes to Quinn’s cottage. Quinn is frantically looking for the tracker given to him in the caves. He tells Dawson about the wounded creature, and Dawson tells him about the UNIT soldiers rushing off to the farm. Quinn thinks the creature must be there and heads off.
The Brigadier, The Doctor and the UNIT soldiers manage to break into the barn and find Liz unconscious. Hawkins and another soldier search the top floor and almost shoot a chicken. Hawkins says there’s no trace of the creature, except that the door was bolted from the inside. Liz starts to regain consciousness. Hawkins finds a back door which the creature must have escaped through. The Brigadierorders a full search around the barn. The Doctor asks Liz what the creature looked like, and she says it was a reptile that walked upright. Quinn arrives in the barn. He says he was just passing and saw all the fuss. He tries to question Liz as to what the creature looked like, but The Doctor doesn’t allow her to tell him. Quinn stops by but, seeing there are too many people around, tries to slope off. However, the Brigadier asks for his help with local landmarks.
The UNIT soldiers have started their full search using dogs and helicopters.
Quinn offers his help and then leaves. The Doctor asks him if he could give Liz a lift back to the headquarters. Quinn changes his story and says he needs to head into town to the garage first. Once he has left, Liz points out that the barn isn’t on Quinn’s way from the cottage to the headquarters — so why was he passing?
Quinn pulls up in the middle of the moors and switches on the tracker. The search dogs in the area go crazy. A helicopter passes at low altitude. Quinn hides the tracker and gets back in the car.
The Doctor and the Brigadier join the search. Hawkins receives reports from the helicopter that it’s seen a man in the same place as a strange noise was detected. The Doctor and the Brigadier head off in Bessie to explore.
Quinn has moved on and turns the tracker back on. The beeping builds up rapidly. The creature is approaching Quinn rapidly from behind.
All of a sudden, the noise stops. The Doctor and the Brigadier have reached the area from where it was emanating. They find the tracks of a reptilian biped and car tracks. The Brigadier focuses his search on this area.
Back at headquarters, Baker has gained consciousness and is eager to join back up with UNIT, but Liz says he is not well enough yet. He remembers everything that happened in the cave up until the moment he was attacked. He is insistent he wants to join back up, but Liz refuses. As soon as she leaves, he begins to dress himself.
The doorbell at Quinn’s cottage rings. It is The Doctor. He questions why Quinn is neither at the garage nor at the centre. Quinn tires to pacify him and send him on his way, but The Doctor forces his way in. He notes how warm it is in the cottage. Quinn says the thermostat is broken. The Doctor comments on it being like the reptile house at the zoo. This rattles Quinn, who asks The Doctor to leave. The Doctor tells Quinn to let him help, but Quinn just shows him out.
Liz and the Doctor are in Quinn’s office and are looking through Quinn’s files. The Doctoropens a locked cabinet and finds a strange ball and some notes. Liz inspects the ball and sees it is some kind of globe. The Doctor inspects it and says it is a representation of the world before the Great Continental Drift, two hundred million years ago. He has also deduced that the notes are calculations to do with the age of the Earth during its Silurian period. Dawson interrupts them. The Doctor reveals his suspicions to her and implores her to tell him what she knows. She is about to tell all when they are interrupted by the Brigadier. Dawson apologises to The Doctor and leaves. The Brigadier asks The Doctor about Dawson, but The Doctor just says, “Never mind.”
Quinn’s doorbell rings insistently. He leaves it, and whoever it is lets themselves in. It is Dawson. She tells of the Doctor and the fact he knows more than they thought he did. She implores him to tell someone. He refuses, saying The Doctor will want to steal the scientific discoveries that he will gain. She gets cross and says he hasn’t gained any scientific knowledge. He confides he has one of the creatures locked up and isn’t going to return it until it gives him the knowledge he requires.
In a meeting at the centre, The Doctor confirms that the interference affecting the power is coming from the caves. Baker enters and demands they move in the caves in force. The Doctor disagrees. The Brigadierorders Hawkins to take Baker back to the infirmary. Lawrence is peeved that the Brigadier is”arresting” his staff. The Brigadier says he agrees with Baker and that they should use force in the caves, but Lawrence says he has very little time to take action on this as he has sent for the Permanent Under Secretary, Masters, who is coming to inspect UNIT’s operation and potentially call the Brigadier back. The Brigadier pursues Lawrence, arguing. The Doctor heads off to Quinn’s cottage to convince him to trust him.
Quinn’s doorbell again goes unanswered. The Doctor lets himself in and looks round. He finds Quinn unmoving on a chair with the tracker in his hand. The Doctor inpsects Quinn, who he realises is dead. He examines the tracker and turns it on. A reptilian humanoid enters the room and confronts The Doctor.
The Doctor offers the creature his hand. He asks if it is a Silurian. It nods in agreement. He asks what help he can offer it and how many of his species are in the cave system. The Silurian hears an approaching car and runs.
Baker is examining a map on his hospital bed. He hides it away when his guard, Sergeant Hart, turns to look at him. Baker calls Hart in and asks him for help taking off his jacket. As he does, he knocks Hart out and runs.
The Brigadier is furious with Hart. Hart asks if he wants to summon up a search party but the Brigadier declines, saying that he expects to find Baker in the caves — they will find him when he and the UNIT soldiers enter.
Baker is, indeed, in the caves. As he explores, he gets trapped in some water that begins to froth. Two Silurians approach. Baker fires at them until he has run out of bullets. The Silurians produce a noise that immobilises him.
Liz tries to dissuade the Brigadier from military action. The Doctor enters and reaffirms Liz’s point — he says that the establishment should be closed down and a scientific investigation should go ahead in lieu of an invasion. When left alone, The Doctor tells Liz that Quinn is dead. When asked why he didn’t tell the Brigadier, The Doctor explains it would have further provoked him into military action when he believes that the Silurians only attack when cornered. The Doctor says he is to go to the caves to talk to them. Liz insists she come too. The Doctor shows Liz a map he found in Quinn’s office that has a route written out on it.
The Doctor and Liz follow the route. Liz points out a more direct route they could take. As they go off to follow it, The Doctor discovers bullet cartridges and Baker’s pass. He throws a rock into the puddle before them which begins to froth. They decide to stick to Quinn’s route. As they walk, Liz expresses concern as to how hot it is. Soon enough they discover a doorway. They hear a Silurian approaching and hide. The Silurian comes to the door and emits a beeping noise which causes it to open. The Doctor and Liz inspect the door. Liz finds that it is boiling hot. The Doctor tries the scanner that he took from Quinn. It opens the door. They sneak in and find a group of Silurians working at a workstation. As they explore, they find Baker in a cage. Baker asks if they have brought the army with them, but The Doctor says he hasn’t. Baker says it is an electric lock and he cannot escape, and tells them that he hasn’t been harmed and that they have just been questioning him regarding the population of the Earth, weaponry and food. The Doctor tells Baker to cooperate with them for the time being, but a humming noise draws the attention of the Doctor and Liz. They observe some kind of apparatus that is reviving a Silurian from deep hibernation, and the Doctor wonders if this explains the power losses. Baker implores them to run. They agree, promising to return. As they leave the way they came, they are met by three Silurians but manage to sneak away unseen. As they try a different corridor, they come across the dinosaur that attacked The Doctor in a cage.
There is a further issue with the cyclotron. A technician named Travis is having to deal with it in lieu of any of the other staff. Lawrence enters and enquires as to the whereabouts of Quinn and Dawson, but Travis has had no reply from eitherof them. The Permanent Undersecretary, Masters, arrives. Lawrence shows him through to the conference room. Masters questions the usefulness of the cyclotron and whether it is living up to the hopes that Lawrence had for it. Lawrence shifts the pressure towards UNIT, highlighting The Doctor’s theory about monsters. Lawrence implores Masters to withdraw the Brigadier and UNIT, but he refuses. The Doctor enters and interrupts Lawrence criticising UNIT. He asks if there has been a power surge recently. The Brigadier enters and asks Masters when he is getting his reinforcements. He tells him that he will not be getting any as he cannot justify such manpower with no pro of. The Doctor says there is no need for reinforcements as he knows what is going on. Everyone concerned asks him to share his knowledge.
Two Silurians are questioning Baker. They ask if humans are the only intelligent species and whether all people carry the projectile weapons that he had. Baker refuses to discuss anything regarding weaponry. The younger Silurian threatens him, but the olderone stops him. The two Silurians argue. The youngerone wants to kill Baker and any humans that they find, but the olderone wants to study them.
After The Doctor has told everything he knows, he is met with disbelief from Lawrence. The Brigadier asks if he has any idea of their weaponry and number. The Doctor questions Masters as to whether this is a government matter so as to stop any rash actions by the Brigadier. He replies that, as yet, there is no pro of. The Doctor argues that they shouldn’t fight and that he is willing to go as an ambassador to discuss with them. Dawson enters and tells everyone that Quinn is dead and admits he knew about the creatures and was keeping one prisoner. The Brigadier says this is pro of that the creatures are hostile. Masters agrees, and they decide to move in first thing in the morning. Once left alone, The Doctor tells Liz he is going to sneak into the caves and warn the Silurians. Liz asks him to be safe.
The Doctor enters a packed room of Silurians in an attempt to warn them. They do not allow him to talk and drag him to a cage near Baker. Once in the cage they ask him why he is there. He says he is there to warn them. Baker tries to stop him. The Doctor tells the Silurians everything and implores them to meet any humans in peace. The Silurians suggest they will not — they say the planet belongs to them and that the humans have stolen it from them.
The Brigadier, Captain Hawkins and the UNIT soldiers are following a map through the cave system but have gotten lost. They turn back the way they came and find a wall blocking them that wasn’t there before.
Baker and the Doctor argue in the cave. The young Silurian enters and tells The Doctor that he has destroyed the soldiers and that he will now destroy them. The young Silurian’s third eye produces a high pitched noise and begins to glow red, causing The Doctor to twist in pain.
The young Silurian is stopped by the leader of the Silurians. The leader rails at the other Silurian for attempting to kill The Doctor and is further angered when the younger says he trapped the soldiers.
UNIT Private Robins is trying to contact base but to no avail. The rest of the soldiers are chipping away at the rock, but it is too thick, and Hawkins says they will need explosives. The Brigadier is concerned as they only have two or three hours of oxygen left.
Liz is showing Masters the findings of the Doctor. He is impressed. Lawrence is still arguing that it is all poppycock. The phone rings, and Masters is told that the soldiers at the cave mouth have lost contact with the Brigadier and his team.
The Doctor tries to talk to the leader of the Silurians. He warns of the armoury that man possesses. Baker tries to silence him, but the Silurian demobilises him and frees The Doctor.
The air is running out in the cave. One of the UNIT soldiers, Robins, is beginning to act strange.
Masters is told that there is no trace of the Brigadier and his men. Dawson enters and says that more men and more equipment should be sent for to free them. Liz wants peace and mentions that it is what The Doctor would want. Masters realises that The Doctor is not there and asks Liz where he is.
A scientist Silurian is analysing Baker’s rifle. The young Silurian comes in and rails against the leader of the Silurians, criticising him for freeing The Doctor.
Liz tells Masters that The Doctor went down before the Brigadier. Lawrence and Dawson say that this is why the UNIT soldiers have been trapped and demand a further attack. Masters errs on the side of caution.
The leader of the Silurians tells The Doctor that the Silurians chose to live underground due to an approaching planet. They suspended themselves in hibernation to survive. The Doctor says that this small planet became the Moon and was of no danger to them.
Baker awakes. He tries to engage a Silurian and ask him where The Doctor is, but he is ignored. Baker screams that The Doctor is a traitor.
The Doctor hears this echo through the cave system. The leader of the Silurians explains that their hibernation system became faulty, and they were only awakened by the introduction of the Cyclotron placed nearby. The Doctor says he is willing to broker a deal between the Silurians and man. He suggests that the Silurians could live in places in which man cannot live due to the heat. The leader of the Silurians agrees to release the UNIT soldiers in return for The Doctor trying to broker the deal.
Robins is now clawing at the walls. Hawkins tries to help him, but Robins attacks him. The Brigadier tells Hawkins to leave him be.
The leader of the Silurians activates a computer.
The wall parts in the cave, freeing the UNIT soldiers.
The Doctor thanks the Silurian leader and shakes him by the hand. The young Silurian comes in and loses his temper at the leader of the Silurians for freeing the soldiers. The leader states that they are to accept the men as equals and the younger Silurian storms off.
The scientist Silurian is studying the evolution of man when the young Silurian enters, asking him to join his rebellion. The scientist is unsure, but the youngerone threatens to kill him. The scientist gives the rebel a vial of bacteria that they used to use when men were monkeys to kill them off. They decide to experiment on Baker with it. They free him, and he tries to escape. He is caught and fights back. He turns down a corridor and is confronted by the dinosaur. Eventually he is knocked out.
Everyone at the research centre is waiting for news of the UNIT forces. Lawrence sarcastically asks if they are to send a search party after the search party. Dawson wants more men to attack. The Brigadier enters and explains what went on. Lawrence still disbelieves. They tell the Brigadierof the Doctor’s movements.
The leader of the Silurians leaves The Doctor sealed in the computer room while he goes to tell the other Silurians of the plan.
The young Silurian wakes Baker in a cave. He looks around, confused, and the Silurian watches him escape.
The leader of the Silurians is furious at the young Silurian for infecting Baker. The leader says he will destroy him if he defies him again.
The Doctor is studying the Silurian civilisation on a computer. The leader returns and tells The Doctor of the infection. The Doctor is told that there is no cure, but he is given a vial of the bacteria for his scientists to experiment on. The Doctor is then released.
The Brigadier reassures a concerned Liz that The Doctor will be all right. Baker enters and claims that The Doctor is a traitor working in cahoots with the Silurians and says they must attack. The Doctor enters and says that this is the opposite of what they should do and orders everyone to keep back from Baker. He tells Baker he is infected with the disease. Baker doesn’t believe him and attempts to arrest him. The Doctor gets up on a table and points at Baker’s wrist. Baker rolls up his sleeve, where there are scabby marks. He faints.
The young Silurian confronts the leader for giving the bacteria to The Doctor. The leader says that they can co-exist with man. The young Silurian disagrees, but the leader says he is in command. The youngerone then kills the leader.
The Doctor says that the Cyclotron must be closed down and put into quarantine until a cure is found. Masters is confused as to why The Doctor still wishes to negotiate, despite the Silurians releasing a disease that could wipe out millions. Liz enters and says that Doctor Meredith has taken Baker to the local hospital. The Doctororders the Brigadier to get Baker back as he will only contaminate more people. Everyone leaves except for Masters and Lawrence. Masters says he intends to leave for London and close the Cyclotron down. As he stands up, he wobbles slightly. Lawrence asks him if he is all right, but Masters dismisses it.
The Doctor and the Brigadier draw up to the hospital in Bessie. They see Baker stumble out of the hospital and fall onto the pavement. The Doctor and the Brigadier examine the body. The Doctor confirms he’s dead, and comments that he is”the first one”.
A doctor and a nurse run out from the hospital. The Brigadier stops them from tending to Baker. When The Doctor states he has been killed by an alien disease, The Doctor wants to investigate further, but the Brigadier pulls his gun. The Doctor tells the Brigadier to quarantine the hospital while he returns to the lab.
Later, The Doctor and Liz are experimenting. They have prepared some broad spectrum antibiotics to keep the disease at bay. Liz wants to inject The Doctor. He protests but eventually relents. The Doctor is waiting for a scanning microscope to aid his experiments. The Brigadier enters and says he has quarantined the hospital and ensured all UNIT soldiers have received the antibiotics. Liz informs the Brigadier that everyone that has come into contact with Baker has now contracted the disease, including Miss Dawson. She also states that Lawrence and Masters cannot be found and is asked to go and look. The Doctor tells the Brigadier that he can contain the disease but is unsure if it can be cured. Liz enters and says that Masters has caught the London train. The Brigadierorders Liz to go and man the phones to track Masters. She refuses, saying she is a scientist, but The Doctor tells her to go and she relents.
Masters’ train arrives at a station in London and he disembarks. He begins to stumble, and several people look at him curiously. As he hands the collector his ticket, he falls over. He manages to get back up and gets into a taxi. Just as the taxi leaves, a police car draws up.
The Doctor watches as three technicians set up the scanning microscope. The Brigadier reports they have still not found Masters, but the antibiotics seem to be keeping the disease in check. When asked, The Doctor says he believes the Silurians are lying low to assess the effect of the disease. The Brigadier says that he has placed a UNIT soldier at the mouth of every cave. The Doctor reminds the Brigadier that war should be avoided at all costs. The Brigadier still cannot understand why The Doctor is preaching peace against the creatures that are trying to kill them.
The young Silurian orders the removal of the body of the previous leader of the Silurians. He asks the scientist whether the apes are dead yet. He is told that their resistance is stronger and that they may come up with a cure. The scientist warns that The Doctor is highly intelligent. The young Silurian is dismissive, saying that they are “only apes”.
Lawrence returns and asks Liz where the Brigadier is. He wants to complain about the closing of the Cyclotron and the fact that his staff are being forced to have injections. Lawrence refuses the injections and runs out. The Brigadier enters and receives a phone call saying that the police have missed Masters and that they are beginning a search. The Brigadier is concerned.
Masters leaves the taxi.
Back at the station, the ticket collector that serves Masters collapses, as do several of the other rail passengers.
A UNIT soldier, Wright, stationed in a cave mouth hears a noise. He stands up and yells, but there is seemingly nothing there. When he hears the noise again, he radios to the main party. As he does, a Silurian comes out and kills him.
Sergeant Hart hears this, and Captain Hawkins decides to go see what has happened to Wright despite the fact that it is counter to the Brigadier’s orders. Hawkins and Hart approach the body of Wright. The Silurian hides. It attacks the two soldiers, killing Hart. Hawkins fires several shots into the cave and then retreats.
The Silurians back at their headquarters watch the attack of the UNIT soldiers and are surprised to see how strong they are. They decide to recapture The Doctor as he must be helping them ward off the disease.
The Doctor receives a delivery of a plethora of drugs — a combination of any of those will cure the disease. The Doctor has done all he can analysing the bacteria and sends Liz away for a blood sample of someone infected.
People are now collapsing all over the station. Several police cars and ambulances arrive. A message is broadcast over a police car’s loudhailer, telling passengers not to attempt to leave the station; those who feel ill must stay where they are until help arrives.
Masters is staggering down a sidewalk and is now showing clear evidence of the disease. He collapses and dies, and two policemen find him. They force two passers-by from examining the body.
Liz returns with a blood sample. The Doctor tries his first combination of drugs; it is no good.
The Brigadier is facing pressure to hurry The Doctor and Liz. He stands up for them.
The Doctor and Liz have now tried a numberof drugs, all with no luck. The Doctor is losing confidence. Liz staggers, and the Doctor sends her away for more antibiotics.
The Brigadier tells Liz that Masters is dead and that the disease is all over London. Lawrence enters — he is all pockmarked. He shouts at the Brigadier, saying it is his fault the Cyclotron has been closed and saying it must be a hatchet job from the ministry. He attacks the Brigadier, but as he does he clutches his chest, collapses and dies.
The Doctor is still experimenting. He tries another combination, looks up and says, “Eureka!”
The Brigadier informs Liz that there is a case of the disease in Paris. The Doctor enters and says he has found the antidote. They rush off to try it.
The Silurians have reached the closest point to the centre. They penetrate through the cave wall using their third eyes.
Liz says that the antidote is working on the ambulance man they gave it to. The ambulance man’s temperature has dropped and his pulse is normal. The Doctor says he will telephone the formula to London and rushes off to transcribe it. Hawkins informs the Brigadierof the deaths of Wright and Hart and that the Silurians are advancing everywhere.
The Doctor is transcribing the formula. Behind him the wall glows yellow. Two Silurians break through, and they use their third eyes on him. The Doctor falls to the floor.
The Brigadier is informed by Private Upton that there has been no further news from the soldiers in the cave. Liz says that the ambulance man on whom they tested the vaccine is nearly cured.
The Silurians carry The Doctor away but are seen by Private Upton. Upton yells for assistance but is killed. The Silurians re-enter the cave system and seal up the wall.
The Brigadier and Liz are stalling the Ministry of Defence, who are waiting for the formula to the vaccine.
Hawkins finds Upton’s body and sees the scorch mark on the wall.
Liz goes to look for The Doctor and finds signs of a disturbance. She collects all the papers up off the desk. She tells the Brigadier everything. She also tells him that she doesn’t know which piece of paper has the right formula. Hawkins enters and reports Upton’s death and the scorch mark on the wall. The Brigadier hurries off with Hawkins. Liz looks through the papers and thinks she has found the right one. She picks up the phone.
The young Silurian and the scientist question The Doctor as to how many humans survived. The Doctor says all of them as he has found a cure. The young Silurian tells The Doctor of the death of the leader and tells The Doctor he is the leader now.
The Brigadier re-enters and orders all the men into the cave system and the centre evacuated. Liz says she has told the Ministry of Defence the formula.
The UNIT soldiers are pinned down in a battle with the Silurians.
The young Silurian and the scientist tell The Doctor that it is their intention to render the Earth uninhabitable and that they need the power from the Cyclotron. The Doctor tells them that the generator has been closed down. The Silurians tell The Doctor he will help turn it back on.
As the Brigadier and Liz talk, the electricity to the Research Centre is shut off. The Brigadier expects that this is the beginning of a show of force from the Silurians.
The young Silurian tells the scientist that he is taking The Doctor to the Research Centre and that, as soon as there is power, he is to reanimate all the Silurians.
The Brigadier wants to go to the Ministry of Defence for more men, but he discovers that the lift isn’t working. As he and Liz deliberate what to do, the wall behind them glows red. The Doctor enters, flanked by Silurians. They order the Brigadier to put his weapon down. Hawkins is investigating the lab and overhears. He takes up a position beside the door. The Silurians want to kill the Brigadier and Liz. The Doctor says that Liz is a scientist, and he will need her help. The Silurians see that the Brigadier is a soldier and go to kill him. They are distracted when Hawkins jumps out and fires at the Silurians. Hawkins is killed by the Silurians. The Doctor says that if the Brigadier is killed, he will withdraw his help. The Doctor is led away. As they enter the Cyclotron room, the Silurians kill two of the technicians but are stopped by The Doctor before they can kill more. He reassures the technicians that if they do what they are asked, they will not get hurt. As everyone sets off working, the Brigadier asks The Doctor what he is doing. The Doctor tells him to keep out of the way. The Silurians order The Doctor to attach a device to the Cyclotron. He asks what it is, and he is told by the scientist that it is a molecular disperser that will convert the nuclear power into micro waves which they will fire into the Van Allen Belt. The Doctor says that if it goes wrong, it will destroy all life, but the scientist says they can control it. Liz explains to the Brigadier that the Van Allen Belt filters out the sun’s radiation and that without it the Earth will get so hot that everyone will die, leaving the Earth for the cold-blooded Silurians.
One of the Silurians tries to awaken the hibernating Silurians, but the power is still too low.
The Silurians order The Doctor to provide power to the dehibernation unit and activate the disperser. The Doctor says he needs to stoke up the reactor, for which he will need Liz’s help. He says he needs to feed uranium into the reactor. As the Silurians are distracted, he tells Liz that, on his word, she should put all the uranium rods in at once. She tries to argue, but he shuts her down. The Doctororders all technicians to their usual sectors and begins the process of starting the Cyclotron. Eventually he tells the Silurians that there is enough power for the dispenser. The Silurians switch it on and order The Doctor to increase the power. The Doctor tells Liz to put all the rods in. The molecular dispenser blows up. The Silurians turn off the reactor, and the controls explode. The Doctor informs the Silurians that the reactor has permanently overloaded, which will cause a massive explosion and a radiation leak that will last decades. The Silurians say that this means nothing to them as they will go back into hibernation. They leave, leaving the humans to die in the explosion. The Brigadier congratulates The Doctor, who he assumes is bluffing, but he is soon told that reactor is genuinely overloaded. The Brigadier tells The Doctor that the lift isn’t working and that they are stuck.
In the Silurian base, the scientist tells the young leader that the hibernation unit has malfunctioned and needs someone to switch it on from the outside. Despite knowing that this will mean his death, the young leader volunteers. He says that when they awake, the scientist should be the new leader and implores him to destroy the apes.
The Doctor is fiddling with wires under the control panel of the reactor, but he cannot override the system. Just when all is lost, he realises that he can fuse the control of the neutron flow. He orders the Brigadier and Liz to move back and cover their eyes. There is an explosion and the reactor stops.
Later, The Doctor is back in the cave system. He begins to inspect the hibernation unit when the Young Silurian appears. He suspects that The Doctor tricked them and will reanimate the Silurians once he has killed The Doctor. The Brigadier appears out of nowhere and shoots the Young Silurian. The Brigadier berates The Doctor for being in the cave system alone. The Doctor says he wanted to inspect the hibernation unit so that they can start to reanimate the Silurians one by one and reason with them so as to unlock their technological potential. The Brigadier looks unsure.
Later, the Cyclotron is back up and running, and the Doctor and Liz are setting off to London for some equipment to inspect the Silurian headquarters. He orders the Brigadier to not let anyone in the cave system. As soon as The Doctor and Liz leave, the Brigadier asks Corporal Nutting if the explosive charges are set. He intends to seal the Silurian base permanently.
The Young Silurian is badly wounded but still alive. He staggers to his feet and begins the reanimation process.
Out on the road, Bessie won’t start. The Doctor pours something from a test tube into the gas tank. A low rumble emerges from the car before it kicks into life. Suddenly, a explosion occurs.
The Young Silurian staggers before falling under the weight of the cave falling in.
The Doctor looks on as he realises that the Brigadier has blown up the Silurian base. He asks Liz if she knew. She says she didn’t but knew the government was scared to keep it open. The Doctor says that it is murderof a whole race of beings. With a grim expression, he and Liz set off in the car.