A bored New Jersey suburban housewife's fascination with a free-spirited woman she has read about in the personal columns leads to her being mistaken for the woman herself.

Novelist Catherine Tramell is once again in trouble with the law, and Scotland Yard appoints psychiatrist Dr. Michael Glass to evaluate her. Though, like Detective Nick Curran before him, Glass is entranced by Tramell and lured into a seductive game.

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.

A bored suburban housewife, seeking escape from her life, suffers amnesia after an accident, wakes up, and is mistaken for a free-spirited New York City drifter named Susan.