Paul McGann (The Doctor), Olivia Vinall (Sheena), Nimmy March (Rupa Maguire), David Ganly (Quarren Maguire), Sean Murray (Captain Darvor), Hywel Morgan (Koloth/Jefferson), Laurence Kennedy (Purser Lunney/Aymor/Chancellor), Rakhee Thakrar (Bliss), Nicholas Briggs (The Daleks)
The Doctor and his companion, Sheena, land the TARDIS on the glamorous luxury space-liner Theseus just as it’s about to leave the Jupiter space-port. An opportunity for a holiday presents itself – and it’s one they’re very glad to take.
But when a disturbance catches their attention, they realise sinister events are taking place on board. Passengers are vanishing on every trip. And unless they’re careful they may be next.
Can The Doctor and Emma solve the mystery? Or is there something else they should be worrying about?
In his TARDIS, Commander Aymor of the Third Temporal Battalion contacts the Capitol and reports that he is the sole survivor of his squad, having been ambushed in the Time Vortex. He is managing to keep ahead of the attackers, but he is dying and unsure about whether or not he will be able to regenerate. He informs the Capitol that he has located the target and, after losing contact, heads after the target by himself.
The Doctor and Sheena materialise facing a wall in a broom cupboard and, squeezing out of the TARDIS, find that they are on the Theseus, a cruise liner about to leave the Jupiter Spaceport. Sheena is amazed by the view of Jupiter and how the ship has its own atmosphere, eliminating the need for windows to look outside; as this is expensive, The Doctor surmises that they are on a luxury cruise and decides that they will stay to relax and enjoy mocktails. Showing Purser Lunny his psychic paper instead of a ticket, he learns that they are headed to Vulcan.
When Purser Lunney goes to deal with a man who wants to speak to somebody in charge, The Doctor and Sheena follow and hear that the man has been trying to find out why his sister disappeared after boarding the ship in May. Purser Lunney takes him to have a word with Captain Darvor to discuss the matter. Although Sheena is willing to believe that it is a simple missing persons case, The Doctor is reminded of a similar situation at an airport in the 1960s and wants to investigate. Sheena reminds him that they are on holiday and should enjoy themselves for once, so they run up to the next deck to have the best view of the launch.
The Doctor and Emma budge up so that Quarren and Rupa Maguire, a married couple on a budget holiday, can enjoy the view as well. The Theseus takes off and jumps into hyperdrive, raising shields to protect the minds of those aboard from being driven mad by the sight of hyperspace. The two pairs part ways, with Rupa suggesting that they might all have dinner together tonight. The Doctor took notice that the man taken to the Captain had not been escorted off of the ship before take-off and goes to investigate with Emma, heading to the crew quarters seven decks down and gaining access by convincing Jefferson that they are escapologists in the cabaret.
Overheard by The Doctor and Louise, Captain Darvor argues with Purser Lunney about how they are asking for trouble by selecting people with relatives as prize winners. Purser Lunney says that precautions are taken but that no system is infallible. The Doctor and Louise reach the engines and hear the man calling for help; they find him inside an energy transfer unit ready to absorb his life force and learn that his name is Koloth. The Doctor bluntly tells him that his sister was most likely killed by the device and the three of them run in the direction of the TARDIS.
The Doctor calls his companion Emma and Sheena but, with some hesitation, she says that her name is Louise. The Doctor realises that he cannot remember where he and Louise met or how long they have been travelling together, but Louise says that it is more important to find the man that they came in search for. The Doctor is confused, thinking that they had already done so. They hear Koloth shouting for help and watch as Captain Darvor and Purser Lunney tell him that they are sacrificing him in payment of the toll for using this route through hyperspace; as a troll comes to devour Koloth, The Doctor and Louise emerge and try to force the Captain and the Purser to save him. They are unsuccessful and, marked as the next sacrifices, flee.
The Doctor suggests that they hide by mixing with the refugees as the Captain and the Purser will not want to ruin people’s cheap holidays by shooting them in front of everybody. However, Louise says that the ship is a repurposed liner and that nobody aboard is going on a holiday. The Doctor realises that something is wrong with time and reality and asks Louise what the refugees are running from; he turns to her and finds that he is alone, being told by Quarren and Rupa that he was talking to himself and remembering that he came on his own. Quarren and Rupa corroborate this and tell him that he said that he lost somebody in an attack before arriving.
Captain Darvor arrives and the Doctor draws his sonic screwdriver, brandishing it as a weapon. The Captain says that it was just him below deck and that the dead refugee had been a volunteer; the requirement of sacrifices is publicly known and was accepted as necessary to escape the warzone. The Doctor considers it unacceptable and offers himself as a sacrifice, believing that his many lives might be enough to get the refugees where they need to go. The Captain, Quarren and Rupa are aghast to learn that he is a Time Lord, making him remember the Time War and recognise that reality has been changing, also remembering that he was indeed with a girl. The proximity alert sounds.
The dying Commander Aymor has decided that he will have to kill the renegade in order to keep him from the clutches of the enemy. He braces himself for impact as his TARDIS approaches the Theseus.
The Doctor suggests that Captain Darvor evacuates everybody to the life pods and, when a Battle TARDIS approaches, to raise the hyperspace shields to keep everybody from being vented into space as a result of its arrival. Maguire recognises the Battle TARDIS, but The Doctor asks him to stand aside so that he can speak with the pilot himself. Commander Aymor emerges, looking for the renegade who will not fight, but, before he can fire his staser, he collapses and dies. The Doctor guesses that regeneration inhibitors had been used. The crisis is not over, however, as The Doctor believes that the enemy will be close behind.
The Daleks detect that Commander Aymor’s TARDIS has exited the Vortex and landed about the Theseus, leading them to determine that The Doctor is there. The command is issued for an attack to capture him.
The evacuation begins and the Doctor urges the Maguires to leave as well, warning them that the Daleks will soon be here and that it is his fault. A number of Dalek ships arrive, blocking the way to the escape pods, and the three of them flee as the Daleks disembark and begin to exterminate those aboard whilst searching for The Doctor. The Doctor takes the Maguires to the broom cupboard and finds that his TARDIS is missing.
The final shuttle leaves the Theseus, but the proximity alarm alerts them to a Dalek ship materialising ahead. Not detecting any Time Lord life signs aboard, The Daleks destroy the shuttle.
To stop the Daleks from destroying any more escape shuttles, The Doctor decides to give himself up in order to buy them time to escape. He contacts the Dalek ship and invites them to come for him, having rerouted the transmission signal to make them think that he is at the bridge so that he and the Maguires can find a way to escape. The Daleks soon locate them, but the trio are saved by Bliss, a scientist with a regression weapon taken from a dead trooper. She is leading a group of people which includes Jefferson, who has no memory of having met The Doctor before. The Doctor tells them that they will escape on one of the Dalek timeships.
The Squad Leader reaches the bridge and reports to the Dalek ship that it is empty. However, there has been no activity in the Vortex and the Doctor must still be aboard.
The Doctor and Bliss enter a Dalek timeship to make sure that it is empty whilst Captain Darvor confides in Jefferson that he is going to sacrifice himself to summon the trolls to kill all Daleks aboard. Bliss shoots and seemingly kills a Dalek using the last of her weapon’s power and goes to fetch everybody whilst The Doctor works out how to fly the ship. Once everybody is aboard, he takes off. The Daleks detect this and begin pursuit, but they find that the Theseus is going into hyperspace and go to the bridge to exterminate Captain Darvor and stop him. The troll appears and destroys the Daleks, whose weapons have no effect on it.
The Doctor crashes the Dalek ship on a jungle planet and says that they will have to be on the move to make sure that they are not followed. The ship requires substantial repairs as well as new doors before it can be used again. The Dalek in the ship turns out not to be dead and emerges, saying “exterminate”.
This story’s title and concept is based on the Ship of theseus paradox, which questions whether an object, if all its components are replaced, is essentially the same object. This idea would later be referenced in regards to the Half-Face Man from Deep Breath
The Doctor materialises the TARDIS facing a wall. The Tenth Doctor would later materialise facing the side of a rubbish bin. (Fear Her)
The Doctor muses that the last time he heard of missing passengers on a flight was at an airport in the ’60s and it turned out to have a very unconventional explanation then as well. (The Faceless Ones).