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.