Invisible aliens in a tiny flying saucer come to Earth looking for heroin. They land on top of a New York apartment inhabited by a drug dealer and her female, androgynous, bisexual nymphomaniac lover, a fashion model. The aliens soon find the human pheromones created in the brain during orgasm preferable to heroin, and the model’s casual sex partners begin to disappear.

Roberta is a bored suburban housewife who is fascinated with a woman, Susan, she only knows about by reading messages to and from her in the personals section of the newspaper. This fascination reaches a peak when an ad with the headline “Desperately Seeking Susan” proposes a rendezvous. Roberta goes too, and in a series of events involving amnesia and mistaken identity, steps into Susan’s life.