When Professor Evans of the Astronomical Institute detects the arrival of the Medusan spaceship Nemesis on Earth, his assistants, Rudi Schmidt and Liz Becker set off to investigate the ship, but while inside the vessel, Rudi accidentally activates a device and is blinded. Meanwhile, the escapees Adam and Shem explore their new surroundings in an attempt to find sanctuary from their Medusan oppressors. Having failed with their earlier attempt to make contact to a herd of cows, the two men discover that the dominant life-form also has a humanoid form – and females.

Octavia takes the damaged Nemesis ship back into space to have repairs carried out on it, taking Liz and Rudi with her as hostages. In exchange for the lives of the two humans, Fulvia demands that Adam and Shem return home with her, but the two Medusan men refuse, unless they can return to their homeworld as equals with the females. Liz and Rudi arrive on Medusa, were Rudi is put to work, while Liz is introduced to a life of luxury.