Some time has passed since the Doctor and the Ponds enjoyed Christmas together. Amy and Rory are in the middle of an icy divorce when people around them suddenly grow Dalek eyestalks and zap them onto a spaceship. The ship is the Parliament of the Daleks, and the Doctor has been similarly summoned before the Prime Minister Dalek. The Daleks explain that they need the Doctor to save them, which is kind of a twist. There’s an asylum planet where they’ve sent all the craziest, most uncontrollable of their kind and they need the Doctor to get down there and deactivate the force field because they’re too scared to do it themselves. They brought Amy and Rory along because “the Doctor needs Companions,” but really, they probably just want those crazy kids to work things out.
Also down on the planet’s surface is a crashed cruise ship. Its seemingly lone survivor is a chirpy, flirty young woman named Oswin Oswald. She’s been holed up somewhere beneath the surface, hacking into Dalek systems, listening to Georges Bizet and making crummy soufflés. The extra dangerous thing about this planet is its “nanocloud,” which turns any living or dead tissue into truly creepy Dalek puppets. How Oswin has survived this perplexes the Doctor. He and the Ponds have special bracelets to protect them against the cloud, but Amy’s is ripped off during a scrape with the puppets. The cloud messes with her memory and perception. Part of the process involves stripping away love, so Rory volunteers to give her his protective bracelet. As he explains, he’s always been the more invested of the two, so it will take longer to strip away his love. That’s when Amy breaks down and finally admits the reason she filed for divorce is because she can’t have babies and Rory wants babies so she decided to “set him free.” So dumb and contrived. Bah!
Meanwhile, the Doctor is trying to track down and rescue Oswin. He’s a bit suspicious of her, but she keeps saving him and proving she’s kind of more awesome than her initial introduction would seem to suggest. When a group of super-duper crazy Daleks go after the Doctor, she erases him from their memories. Just when Oswin begins to pack for what she’s sure will be a grand adventure, the Doctor discovers the awful truth: Oswin is herself a Dalek. When the cruise ship crashed, she was taken for her genius hacking skills. She’s been clinging to the scraps of her humanity, creating fictions – like her soufflés – to keep her sane. The Doctor has to leave her behind, but they accomplish their mission and turn off the force field. She and the insane Daleks who imprisoned her are destroyed.