A solar tsunami sends the TARDIS hurtling towards a futuristic factory on Earth, where human doppelgangers are used to mine dangerous acid, as the time-travelling adventures continue.

A second wave hits and the "Gangers" separate. They can remember every second of their "original's" life and feel every emotion they've ever experienced. But are these memories stolen or have they been bequeathed? Are the Gangers merely faulty machinery that must be shut down or are they living, breathing, sentient beings? Can the Doctor convince the terrified humans to accept these "almost people" and prevent an all-out civil war before the factory explodes?

As the solar storm rages, Jennifer, a Ganger driven mad by the memories of being "decommissioned", is seeking revenge, as the time-travelling drama continues.

She can remember every excruciating second of every "execution" and is determined that the humans will pay. And she isn't just talking war; she's talking revolution. As the crumbling factory fills with toxic fumes and drips lethal acid, the "Originals" wait desperately for the shuttle from the Mainland to rescue them. But Jennifer has other ideas. Can the Doctor convince the terrified factory workers to embrace their own humanity and work together with their Gangers to overcome a monster of their own making?