A Humanoid Dalek

The Doctor is lured to the ruins of Skaro, the original homeworld of the Daleks, by a woman called Darla who asks The Doctor to save her daughter from a Dalek prison camp. However, The Doctor realises that this is all a trap: unbeknownst to Darla, she has actually been converted into a sleeper agent of the Daleks. When The Doctor informs her of this, her programming becomes active, and she stuns The Doctor, just as a Dalek saucer arrives to take him to the Parliament of the Daleks. There he is reunited with Amy and Rory, who have been similarly kidnapped from present-day Earth, just after Rory has delivered Amy their divorce papers at one of her photo shoots.

Within the Parliament of the Daleks, and much to The Doctor’s surprise, the assembled Daleks don't exterminate him. Instead the Daleks want him to save them. The Prime Minister of the Daleks explains that the Daleks have a planet known as the Asylum, where they dispose those of their kind who go wrong: the insane, the battle-scarred and the uncontrollable. The Daleks though are unwilling to engage with the inmates themselves, as destroying such pure hatred face-to-face would contravene their sense of ‘beauty’, much to The Doctor's revulsion.

The Daleks have captured The Doctor because they have received an unknown transmission from the Asylum which The Doctor recognises as being "Habanera" from the play Carmen. It is from a woman, Oswin Oswald, who claims to be on board the Alaska, a spaceship which has crashed into the Asylum, and who has been fending off Dalek attacks for a year.

Parliament of the Daleks

The crash of the Alaska has ruptured the planet's force-field and so is risking the escape of the planet's inmates. A planet of insane Daleks roaming free is something that scares even the Daleks and is something that they want to prevent. The Parliament of the Daleks therefore now wishes to destroy the planet remotely, but the force-field has not been ruptured sufficiently to allow this. The force-field can only be deactivated from the planet itself but, afraid to face such a mission themselves, the Parliament of the Daleks task The Doctor, Amy and Rory to do this for them.

Despite protesting The Doctor and his two travelling companions are given bracelets to protect them from the planet's nanogene cloud, which would convert them into Dalek puppets to serve the facility's security systems. They are then dropped through the force-field breach via a gravity tunnel onto the frozen surface of the planet. The Doctor and Amy land close to each other and are discovered by Harvey, another survivor from the Alaska. Rory, however, is dropped to the bottom of a long shaft directly into the Asylum - there he accidentally awakens some of its inhabitants, but is saved and guided to a safe room by Oswin, who has managed to access the computers.

The Doctor Meets the Daleks

Meanwhile Harvey is revealed to be a Dalek puppet, converted by the nanogene cloud. A similar fate has befallen the corpses of the other Alaska survivors, who re-animate and attack The Doctor and Amy, stealing her bracelet just before the pair are saved by Oswin and guided to Rory. Now unprotected from the nanogenes, Amy begins to be converted into a Dalek puppet and begins experiencing memory loss and hallucinations.

The Doctor guesses that the Daleks will destroy the planet as soon as he deactivates the force-field, before he and his companions can escape. However, he realises that Rory's hideout is a telepad via which they can all teleport back to the Dalek’s spaceship. Oswin though only agrees to deactivate the force-field in return for The Doctor coming to save her – which he agrees to do despite wondering how she has managed to survive unprotected from the nanogenes for so long. She explains that she managed to shield herself from it.

While The Doctor is gone, Rory tries to give Amy his bracelet. The Doctor having previously explained that love slows the Dalek puppet conversion, and Rory justifies that by ‘coldly and logically’ asserting that he has always loved her more than she loves him, thus he would be converted more slowly - reminding her of his 2000-year vigil ("The Pandorica Opens/The Big Bang"). Amy though angrily replies that she loves him equally, but gave him up since she can no longer have children, as a result of the events that took place at Demons Run ("A Good Man Goes to War"), something that she knows Rory has always desired. They then realise that The Doctor has already given Amy his own bracelet but didn't tell them, in order to allow the two to converse and reconcile.

Daleks

Meanwhile The Doctor makes his way to Oswin, venturing through the 'intensive care section', containing Daleks who survived encounters with him. However, as soon as he mentions that they ‘survived’ him, the deactivated Daleks come back to life and corner him against the door leading to where Oswin is trapped. Luckily, Oswin hacks into the Daleks' shared information network, and erases all data on him, effectively leaving them with no memory of him.

On entering Oswin's chamber The Doctor, to his horror, discovers that she has been fully converted into a Dalek. Unprotected from the nanogenes for nearly a year, she could not prevent herself from being converted in order to preserve her genius-level intellect for Dalek use. Unable to cope with her conversion, her mind retreated into a fantasy of survival as a human, which was picked up as the Carmen transmission. Oswin is nearly overcome by a Dalek personality at this revelation, though she still possesses human emotions and is unable to kill The Doctor.

Coming to terms with what has happened to her Oswin fulfils her promise of deactivating the force-field, on the condition that The Doctor remembers her as the human she once was, so allowing the Daleks to destroy the planet – but not before The Doctor is able to return to Amy and Rory and activate the teleport to take them off of the planet and back to the TARDIS, which is on board the Dalek spaceship.

On exiting the TARDIS The Doctor discovers that the Daleks do not recognise him due to his removal from their hive intelligence. He jubilantly leaves in the TARDIS and drops the reunited Amy and Rory back home. He then departs alone, delighting in the Parliament of the Daleks’ closing question to him: ‘Doctor who?’ repeating it to himself for his own amusement.