The TARDIS arrives on Earth during a future ice age.  They find scientists in a base who are trying to use an ioniser to stop a glacier.  A creature is found buried in the glacier and one of the scientists calls it an Ice Warrior.  The Ice Warrion wakes up after it thaws out is reveals that it is the captain of a Martian ship.  They landed on Earth many years ago and the ship is still inside the glacier.  Since Mars is now a dead planet, the Ice Warrior attempts to free his crew so that they can take over the Earth.

The scientists at the base determine that the ioniser may cause the Martian ship to explode.  The computer cannot function without further information on the situation.  Penley, one of the scientists, and the Doctor activate the ioniser.  Instead of a major disaster, the engines explode but they only destroy the Martians.  As a side effect, the glacier is stopped also.