The Doctor presents a physics lecture to students and then one of the students asks what is has to do with crop rotation. The Doctor is getting Earth sick, longing to go back into space. Nardole tells the Doctor he shouldn't because of what is behind the vault but the Doctor ignores Nardole. The Doctor heads off into space with Bill Potts and Nardole. The TARDIS receives a signal from space and goes off to investigate.
The TARDIS arrives on a space ship and soon after getting onboard, the atmosphere is vented of oxygen because it is illegal. All oxygen is supposed to be bought and paid for. The Doctor, Nardole and Bill get into spacesuits which provides them with air to breathe. Bill discovers the suits can talk and names hers Velma.
The three travellers come under attack from Zombies and manage to escape and rendezvous with the crew who are still alive. When the Zombies get close, the survivors have to get out into space to escape. Bill's suit is broken and Bill won't survive in space so the Doctor swaps helmets and in doing so the Doctor becomes blind but everyone has made it out alive.
Throughout the episode, two of the survivors are killed and Bill is captured by the Zombies and turned into one. The Doctor realises what is going on and discovers that the suits are making the Zombies act the way they do in the interests of capitalism. The Doctor disables the suits by telling the suits that death will be expensive. Bill Potts returns to normal after her Zombie state is reversed compared to all the other victims.
Back on the TARDIS, the Doctor discovers he still can't see, he thought the TARDIS could return the sight but although his eyes look normal, he can't see anymore.