The planets of the Arriton system have mysteriously vanished, save for Arriton II. The Doctor and Ace investigate, only to discover they are not alone.
Now captives of the Daleks, the Doctor and Ace soon realise they are not the only prisoners on Arriton II, but what secrets lie within an abandoned shipwreck?
The TARDIS crash lands on a barren ice world and the Doctor locates forgotten cryogenic tombs, whilst Ace discovers that not everyone on the planet is frozen.
The Sea Devils take control of the submarine, intent on using its nuclear weapons in an ongoing war. Can the Doctor stop them from unleashing Armageddon?