The Doctor (Tom Baker) and the newly-regenerated Romana land on a strangely familiar planet and investigate the drilling that is going on there. The Daleks are searching for their creator, Davros (last seen in 'Genesis of the Daleks'), in the hope that he can assist them in their war with the Movellans. The Doctor has to reach the evil Kaled scientist before the Daleks, but just who can he trust?