Nyah, a female commander from Mars heads for London in her flying saucer. She is part of the advance alien team looking for Earth men to replace the declining male population on her world, the result of a "devastating war between the sexes". Because of damage to her craft, caused when entering the Earth's atmosphere, and an apparent crash with an airliner, she is forced to land in the remote Scottish moors. She is armed with a raygun that can paralyse or kill, and is accompanied by a tall, menacing robot named Chani.