Stansfield, an astronaut, is sent to a planetary system 141 light-years from Earth. The trip will take 20 years each way. To save him the ordeal of forty years of loneliness, he is to be placed in (newly-developed) suspended animation. Before leaving, he meets and becomes enchanted by his colleague Sandra Horn in just one evening, but by the time he returned, Horn would be 40 years older and Stansfield would still be young because of the suspended animation.

The time travellers work desperately to both escape the Dalek city and prevent a bloody massacre.