On a giant spaceship, the foursome meets an advanced reptilian civilization planning to seize Earth; with Peter Davison.

The Doctor is captured by the Cybermen; he discovers the source of the signal and learns the full extent of the Cybermen's plans; the very future of the human race is threatened, as this is no war of conquest, but total destruction.

The Doctor fixes the chameleon circuit, sort of, and runs afoul of the Cybermen who have just allied with Lytton.i