In this British sci-fi thriller, a spacecraft from Ganymede, the moon of Jupiter, lands in a small community, and the alien visitors set out to find women. It seems that their population has become dangerously low and they need human females for breeding purposes. When the police begin receiving reports of a number of missing women, it takes quite some time before anyone thinks that there could be a link between the disappearances and a dramatic increase in UFO activities. John Saxon plays Jack Costain, an American scientist investigating the UFO reports, while Alfred Burke plays Police Detective Hartley.