The newly regenerated Doctor (Tom Baker), assisted by Sarah, Harry and the Brigadier, has to track down the theft of the components for a powerful new laser gun, and the death of a prominent politician. Sarah investigates the mysterious Think Tank, where it becomes clear that robot K-1 is being misused by its political extremist masters and the Doctor has to prevent the robot from being used to start an atomic war. Tom Baker's first story as the Doctor.

Another adventure for the sixth incarnation of the intrepid time traveller. The Doctor (Colin Baker) and Peri arrive on the planet Necros to pay their last respects to deceased agronomist Arthur Stengos. They discover that his final resting place - Tranquil Repose - is in fact a front for a Dalek farm run by the Great Healer, who turns out to be none other than the Doctor's old foe, Davros.