Davros has been kept in suspended animation aboard a prison space station but now the Daleks have come to collect him, aided by Lytton and his fake 'policemen'.
After a prison space station holding Davros is attacked, Doctor, Tegan, and Turlough find themselves trapped in a time corridor that forces them to Earth, where they discover a sinister plot is afoot.
Cybermen capture the Doctor and Peri and bring them to Telos, where they plan to use the TARDIS to invade Earth.
On Telos, the Doctor is reintroduced to the Cyber Leader and meets the Cryons, the planet's original inhabitants who will go to any lengths to get their world back.