A space mission goes disastrously wrong and, when the rocket is recovered, two of the crew have vanished without trace, while the third undergoes a bizarre transformation. An alien life form has gained control of his body, and intends to use it in a plot to take over Earth. Sci-fi horror based on the TV series, starring Brian Donlevy, Jack Warner and Richard Wordsworth.

The first manned spacecraft, fired from an English launchpad, is first lost from radar, then roars back to Earth and crashes in a farmer's field, and is found to contain only one of the three men who took off in it; and he is unable to talk but appears to be undergoing a torturous physical and mental metamorphosis.