The final segment of the Key is traced to the planet Atrios, engaged in a long war with the neighbouring Zeos. The Marshal of Atrios intends a final strike to destroy the Zeons, but the Doctor and Romana discover that Zeos is deserted and the war is being co-ordinated by a computer called Mentalis, built by one of the Doctor's old Time Lord Academy friends, Drax.

The Tardis materializes on what appears to be an Edwardian racing yacht.

Turlough tries to commit suicide to escape the influence of the Black Guardian.

The doctor's (Peter Cushing) TARDIS time machine takes him, his granddaughters and a friend (Roy Castle) to war-ravaged planet Skaro.

Dr. Who (Peter Cushing), his granddaughter, his niece and a London bobby (Bernard Cribbins) find that Daleks have invaded 22nd-century Earth and are turning humans into slaves.

The TARDIS falls through a CVE into E-Space and arrives on the planet Alzarius. There the inhabitants of a crashed Starliner and a group of young rebels called the Outlers, led by a boy named Varsh and including his brother Adric, are being terrorised by a race of Marshmen who emerge from the marshes at a time known as Mistfall.

The Doctor discovers the English King is a shape-changing android called Kamelion!

The Doctor discovers that the captain of the pirate ship is actually a concentrated beam of mental energy.

The Doctor manages to eject Wrack and pilot her vessel to victory.