|Written by||Phil Ford|
|Directed by||Gary Russell, Charles Cecil|
|Produced by||Steven Moffat, Piers Wenger, Beth Willis, Anwen Aspden, Charles Cecil, Richard Jenkins, Mat Fidell|
London, the 23rd Century: devastated by a plague of biblical proportions, the city has been consumed by Davy Jones’ Locker. Now the Doctor and his latest companion, Amy Pond, find themselves in a deep sea base. It is a research station designed to study the ruins and salvage some shrapnel of hope from the wreckage. A swarm of monstrous Vashta Nerada have invaded the facility with plans to feast on the crew.
Can the Doctor and Amy survive? Only you can decide….
The Doctor and Amy have come under attack by a giant shark-like creature which batters the outside of the transparent conduits that link sections of the undersea base. they are forced to escape and are left with no option but to move on, as their way back to the TARDIS has been destroyed by the massive jaws of the monster. As they traverse the tunnels, they are stalked by the beast which is trying to break through.
Arriving at the main building, Amy and the Doctor find one of the base’s personnel, Martin Flanagan. Unfortunately, he is trapped in the area because a sentient computer named Jones will not let him in due to the quarantine. The Doctor manages to convince Jones to let them pass through a compromise after giving it recognition for its hard work (something Jones has long wished for).
Inside Poseidon 8, they meet Oswald Fox and Dana Tanaka, who begin to explain the situation. The lights go out, and when Oswald and Dana begin to panic, the Doctor realises there is something else attacking Poseidon 8: the Vashta Nerada. When the lights come back on, to the horror of his coworkers, Martin is found to be dead: there’s nothing left of him but his diving suit and bones.
The Doctor and Amy decide to go fix the generators so that they may keep the Vashta Nerada at bay, all the while avoiding the shark-like Zaralok that continues to stalk them; it attempts to break through the glass, but it proves strong enough to withstand its blow. they arrive to the generator and are faced with two dead divers reanimated by the Vashta Nerada. they avoid them and the generator is turned back on, expelling the Vashta Nerada from the two bodies when the light is restored. The Doctor takes an environment status chip from one of the divers’ suits to have Jones analyse it.
Jones detects that radiation is recorded in the status chip, but is unable to identify what kind it is as it has not records of such radiation. The Doctor deduces that the reason is because it’s Vortron radiation, a type of radiation caused by rifts in time that is not ordinarily found on Earth.
Deciding to focus on curing the disease caused by the radiation, the Doctor asks Oswald to give them the access codes for parts of the base that are sealed off, to allow them to find the ingredients he needs to create a cure.
Cracking under the stress of the situation, Oswald forbids the Doctor and Amy from doing so due to the danger posed by the Vashta Nerada. Oswald explains he plans to send the crew up to the surface in escape pods. However, this is actually a terribly bad idea: if the survivors are not destroyed by the Zaralok, they’ll be fish in barrels for the Vashta Nerada in the darkened pods. However, this thought doesn’t occur to Oswald.
The Doctor and Amy convince Dana to give them the codes, letting them out into the corridors to find ingredients. Finding a series of vegetables recently harvested in the corridors, the Doctor concocts an antidote and gives one of the serums to Dana. Dana reveals another piece of information to the mysterious goings on: all these strange occurrences started with a mysterious flash of light.
The Doctor uses the base’s scanners to search the area for the source of the chaos, locating a nearby shipwreck – but it’s no ordinary shipwreck. It’s the famed US supply ship, the USS Eldridge, which was part of an invisibility project. The Time Lords attempted to stop the project, but failed when the ship fell through a wormhole.
As an unintended result, the experiment caused the ship to bend the laws of physics and travel through time, the electromagnetic generator now acting as a gateway through time and space that brought both the Shark and the Vashta Nerada to Poseidon 8.
The Doctor also finds that there is an underground tunnel back to the TARDIS and prepares to leave with Amy and Dana to the Eldridge. However, Oswald threatens them into being arrested with a harpoon gun. He ties them up and leaves to launch the escapes pods with Dana. Using an escape trick he learned from Houdini, the Doctor gets untied and unties Amy. they use the secret passage and get back to the TARDIS.
The Doctor pilots the TARDIS to the USS Eldridge and tells Amy they have to find the controls for the gateway and deactivate them as it is the only way to remove the Vashta Nerada and Zaralok from Poseidon 8 and return them to their own places in time. It’s easier said than done as Vashta Nerada are on the Eldridge as well, animating the suits of the crew to go after them again. Too make matters worse, the giant shark has found them and is still trying to find a way in to eAt them. Making their way through the ship, the Doctor and Amy outsmart most of the Vashta Nerada by luring them into chambers and flushing them away.
Upon reaching the controls for the gateway, the Doctor and Amy find the room is full of half-broken machinery due to the ship’s rough trip through time. Managing to navigate their way through a safe path, the Doctor and Amy reach the controls for the gateway. Undoing the damage the gateway has caused is now a race against time; the Zaralok is ramming repeatedly against the glass to break into the ship for a meal. However, Amy and the Doctor throw the switches for the gateway, sending the shark back to whence it came along with the Vashta Nerada, also ending the radiation.
Back on Poseidon 8, Dana and Oswald are thankful for their help, with Oswald apologising for his actions and offering to let the Doctor and Amy join their Christmas feast of sea pumpkins.
However, the Doctor and Amy are more than a little unwilling and secretly enter the TARDIS when Dana and Oswald have their backs turned. The sound of the TARDIS dematerialising makes Oswald and Dana turn around to see their saviours are taking off, much to their shock..