The Doctor and Sarah arrive on the planet Karn. There they take shelter in the castle of Dr Solon who is secretly hiding the living brain of the Time Lord criminal, Morbius.
The Doctor is a prisoner of the Sisterhood of Karn who intend to burn him at the stake. Sarah hurries to the Doctor's rescue but pays the price for her efforts.
Sarah has been blinded and the Doctor asks the Sisterhood for help. Morbius, fearful that the Time Lords have tracked him down, tells Solon to install his brain in a new body.
Morbius, housed in a terrifying new body, lives and breathes once more and the Doctor is forced to challenge his foe to a deadly mental duel which only one of them will survive.
