The Master, in the guise of Professor Thascalos, has constructed at the Newton Institute in Wootton a device known as TOMTIT - Transmission Of Matter Through Interstitial Time - to gain control over Kronos, a creature from outside time. The creature is summoned but proves to be uncontrollable.

On Jupiter's moon Ganymede, an alien life-form has taken over the body of a human astronaut, creating an almost perfect copy. It then begins the long return journey to Earth.

In the 26th century, the Doctor and Jo uncover a plot by the Master to provoke an interplanetary war between Earth and Draconia.

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.