The Doctor discovers a bomb planted by the Cybermen, disarms it and then materializes the Tardis onto a freighter orbiting the Earth where mysterious murders are also being committed.

The Cybermen have taken over the bridge of the freighter. They fit a device onto the freighters control panel that will cause the ship to explode. The ships fuel will cause a explosion so strong that it will destroy the Earth completely. The Doctor and Companions battle against the Cybermen in an attempt to foil their plan. Someone pays the ultimate price to save the Earth and crew of the freighter.