Fleeing Cosmo through the Vortex, the TARDIS gets sucked down a temporal plughole, and the Doctor emerges into a weird landscape. Finding other lost souls in the form of mountaineer George Mallory and scavenger Athelia, the Doctor soon stumbles across another, more surprising denizen of this strange dimension - herself!

With Cosmo still in pursuit and memory-stealing winds threatening to wipe her mind for good, the Doctor senses a complex trap in action. But whose trap is it, and how can she possibly escape?