A young woman witnesses a bus accident, and is caught up in the aftermath, where the question of whether or not it was intentional affects many people's lives.
This film tells the story of a successful writer called Harry Block, played by Allen himself, who draws inspiration from people he knows in real-life, and from events that happened to him, sometimes causing these people to become alienated from him as a result.
Marion is a woman who has learned to shield herself from her emotions. She rents an apartment to work undisturbed on her new book, but by some acoustic anomaly she can hear all that is said in the next apartment in which a psychiatrist holds his office. When she hears a young woman tell that she finds it harder and harder to bear her life, Marion starts to reflect on her own life. After a series of events she comes to understand how her unemotional attitude towards the people around her affected them and herself.
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.
