The TARDIS arrives on Earth in a new ice age. The travellers make their way into a base where scientists, commanded by Leader Clent, are using an ioniser device to combat the advance of a glacier.

A giant humanoid creature, called an Ice Warrior by one of the scientists, has been found buried in the nearby glacier. When thawed, it revives and is revealed to be Varga, captain of a Martian spacecraft that landed on Earth centuries ago and is still in the glacier. Varga sets about freeing his comrades and formulating a plan to conquer the Earth.