The Doctor is summoned before a parliament of Daleks, along with Amy and Rory who are now separated. They demand that the trio infiltrate an asylum that contains the maddest and most dangerous of Daleks.
A spaceship containing a mystery woman has crashed into the planet and the asylum has been compromised. The Dalek leaders want the planet destroyed, but this can only be done once the Doctor has found a way inside to deactivate a force field.
The trio are transported to the planet, but the Doctor and Amy become separated from Rory. However, all three receive remote advice from Oswin, the woman on the spaceship.
The Doctor and Amy uncover a Dalek defence system that turns any human, alive or dead, into a Dalek themselves. Amy is consumed by the system and begins to lose her mind. As she and Rory begin to bond, the Doctor has to pass through Intensive Care – an area containing the Daleks who have survived previous encounters with him. Oswin saves the Doctor by wiping the Daleks’ memories of who he is.
However, upon reaching Oswin, the Doctor learns she has long since been turned into a Dalek and has only been dreaming that she is still human.
Oswin fights her Dalek urges and turns off the force field, allowing the Doctor, Amy and Rory to teleport off the planet shortly before it is destroyed. They teleport into the Tardis, which returns them to the Dalek parliament, but the Daleks no longer know who they are and the trio are able to escape to Earth.