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.
In a futuristic world where the polar ice caps have melted and made Earth a liquid planet, a beautiful barmaid rescues a mutant seafarer from a floating island prison. They escape, along with her young charge, Enola, and sail off aboard his ship.