The TARDIS lands on the old Dalek homeworld of Skaro where the Doctor and the newly regenerated Romana discover that someone is digging deep beneath the planet's surface.
Davros has awoken from his centuries long slumber and is taken prisoner by the Doctor before the Daleks can reach him. But the Daleks will stop at nothing to recover their creator.
The Doctor discovers that the Daleks need Davros to break the stalemate in their war with the Movellans, and the Movellans now want the Doctor to fulfil the same purpose for them.
