The Doctor, Jamie and Victoria arrive on Earth in the far future to find that the planet is in the grip of a second ice age. Scientific outposts are scattered across the globe, fighting desperately against advancing glaciers that threaten to send the world back into prehistory.

When a huge armoured figure is discovered buried in the ice, a force more deadly than the ice floes is unleashed - Varga, a Martian Warrior, whose craft crash-landed centuries ago. Reviving his crew, he aims to conquer Earth in the name of Mars.

With power at the outpost sinking to dangerously low levels, it falls to the Doctor to try to save humanity - not only from the warmongering Ice Warriors, but from the barely checked powers of the relentless glaciers.