Thanks to a "solar flare," the Doctor, Amy and Rory wind up in a 13th century monastery in Scotland, but it's slightly in the future. Well, for us, anyway. It's an acid-processing facility of some sort, manned by a handful of contractors. The Doctor pretends to be a meteorologist, sent to inspect the place for damage after the solar wave. The Doctor quickly notices that there are two copies of everyone. It seems the job is so dangerous that the contractors have taken to using a vat of extra creamy yogurt called the Flesh to make dopplegangers of themselves to do all the dirty work. They insist that the "gangers" are simple, unfeeling things that aren't really alive, and can't even exist without being linked to their progenitors. The Doctor, having not only scanned the yogurt but stuck his hand into it, disagrees. When another solar wave comes along and knocks everyone out, the charge also liberates the gangers from their originals. This leads to confusion for the gangers, who possess a lifetime of memories and feelings, and for the originals who can't always tell real from Memorex.
One of the gangers - a copy of a young woman named Jen - is especially confused and frightened. She and the other gangers don't have full control over their forms now that they've been freed, so they periodically look like slightly gooey Voldemorts. Rory is surprisingly brave and tender towards Jen, comforting her even as Amy is distrustful. Rory convinces Jen Copy to let the Doctor help her and the other gangers, but one of the contractors sort of ruins everything by trying to electrocute their copies. It into an "us versus them" thing, with both the copies and the originals fighting for their lives. Meanwhile, the TARDIS has sunk into an acid puddle, the Doctor has lost his shoes, Amy has another sighting of the eye-patch lady and everyone weighs in on the "what makes something alive" debate.
Oh and the yogurt pops out a copy of the Doctor at the end to give everyone a cliffhanger. Stay tuned for the full recap!