While Susan and David try to find a way out of London, Ian and Larry infiltrate the Dalek mine workings.

The Doctor's party investigate the Daleks' central control in Bedfordshire while Barbara and Jenny's attempt to reach it are derailed when they are betrayed.

The Daleks' plan to transform Earth into a giant spaceship and wipe out its inhabitants is nearing completion and the Doctor and his friends face a race against time to prevent them from destroying the planet's core.

The Daleks pursue The Doctor through time and space, with the intentions of exterminating him. Places they land include the Mary Celeste, a haunted house and the empire state building.

While Ian and Vicki are threatened by a Mire Beast, the Doctor and Barbara meet up with the Aridians...who are then ordered to hand them over to the Daleks.