Mysterious forces are at work in 1930s Tibet. The once gentle Yeti have turned savage and besieged a Buddhist monastery. The Second Doctor, Jamie and Victoria arrive expecting a friendly welcome from the abbot, but soon become ensnared in the plans of the extradimensional being known as the Great Intelligence.
Aided by his two assistants Jamie and Victoria, the Doctor lands the TARDIS on Telos, last resting place of the infamous Cybermen. There he discovers a band of archaelogists on a secret expedition to unearth the reason for his old enemies' extinction. In the underground shadowy depths, they find the icy tomb. A whole army in hibernation. A threat to no one, if the temperature remains low. But if the traitor in their midst gets his way, things could really heat up.
The TARDIS arrives in 2070 on the Moon, where a weather control station under the command of a man named Hobson is in the grip of a plague epidemic — in reality the result of an alien poison planted by the Cybermen. Jamie is knocked unconscious and lapses into a delirium, leaving the Second Doctor, Ben, and Polly to fight off a massive Cyberman attack.
The Doctor's TARDIS lands at the Snowcap space tracking station in Antarctica in December 1986. A routine space mission starts going wrong. When the base personnel's suspicions are roused, the Doctor informs them that the space capsule is being affected by the gravitational pull of another planet — a tenth planet in the Solar system.
