The TARDIS materialises on board the Vipod Mor, a galactic survey ship captained by the repulsive Orlous Moston Slarn.

Things are not going too well on board the spacecraft: a mysterious killer stalks the ship's infrastructure; a junior officer, whose body is four years older than his brain, commands its bridge; the craft's computer seems to be developing its own distinctive personality; and Slarn threatens to vent his vindictive anger on his crew.

Soon the Doctor and Peri stumble upon a shocking secret, a secret upon which depends the fate of the entire Universe...

The novelisation of the Radio 4 Doctor Who story.