Returning to the Moonbase, the Doctor confronts Slaar and the remaining Ice Warriors.
A Martian invasion fleet is on its way to the Moon. On Earth, the Doctor fights back.
As the Martian fungus begins to spread, Zoe, Jamie and Miss Kelly attempt to strike back.
On the Moon, the Doctor is captured by the Ice Warriors and learns their plans.
As the world grinds to a halt, the Doctor realizes the Moon is the source of the trouble.
The TARDIS arrives on 21st Century Earth where long distance journeys are made via T-Mat.