The Doctor (Peter Capaldi), Bill (Pearl Mackie), and Nardole (Matt Lucas) follow a TARDIS distress-call to a deep-space mining station. The Doctor expands the Tardis’s air-bubble so they can breathe, but the station soon jettisons the TARDIS’s air because it is unauthorized, and they are forced to put on robotic smart suits to survive. The station operates in vacuum and the suits are the only source of oxygen. The few in the crew that have survived warn that the suits sometimes decide to deactivate the organic components, that is, the humans, to save money. The station is full of zombies—dead but walking around in functioning suits. When the Doctor gives Bill his helmet, he can still breathe, but loses his sight.

When the Zombies touch Bill, she is electrocuted, but still lives. The Doctor realizes that limiting the number of counted human breaths is a cost-saving device. He hacks into the self-destruct system to destroy the station if they are killed. The company computer realizes that this would be bad for profits and recalibrates the oxygen use, taking oxygen from the dead suits and giving it to the living. The Doctor revives Bill, and they recover the TARDIS, then take the workers to the head office to confront the Company. The Doctor is still blind but hides it.

The electronic eyes on the suits resemble those of HAL 9000 and can read lips too. The greed and disregard of human life of the Company compares with that of the Company in the Alien series. The episode was not considered one of the best, though the zombies are scary, and the scene in which Bill nearly dies in vacuum is quite effective.