Journeying across the universe, a space ship begins to experience technical difficulties and is forced to make an emergency landing on Clapham Common, London. A young couple, Oliver and Prudence, arguing nearby; a spotty young man, Willy, reading a porn magazine; and lecherous dog-walker Cliff, are attracted by the bright flashes of light across the sky and all go to investigate. When the ship opens an access door, they climb on board and begin an adventure and a half.

They soon find that the cargo ship is crewed by three aliens of a human-like species that only exists in female form. Fascinated by the three flat-chested human specimens they have encountered, the craft's commander, Skipper, orders crewmates Partha and Cosia to conduct full examinations, wondering if she can sell these curious life-forms to an intergalactic zoo.

Beginning a series of biological, combative and intelligence inspections, the butch, arrogant Cliff is found extremely wanting. He introduces Partha, administering the intellect test, to a skill at which he proclaims his expertise - she is impressed, but proves far too demanding for his abilities and stamina!

Virginal Willy is immediately besotted with both Partha and Cosia, the latter of whom finds him to possess one of the most advanced bodies in the whole universe. When he manages to pass both the combat and intelligence tests with ease the women are astonished, and beyond delighted when he demonstrates human methods of reproduction...