Materialising on an Earth cargo spaceship in the 26th century, the Doctor and Jo are caught up in the tensions between the Earth and Draconian Empires, a cold war that is rapidly becoming hotter. With both sides accusing each other of aggression, the Doctor suspects a third party might be involved. But who would benefit from the devastation of an interplanetary war?

The Doctor and Jo investigate the workings of the TOMTIT machine, a wondrous device created by Professor Thascalos. Neither Thascalos nor TOMTIT are what they seem, and what secret power is locked within the crystal of Kronos