The Longhettis are an Italian-American working class family. Nick (Peter Falk) is a construction worker. He and his wife Mabel (Gena Rowlands) have three children. Mabel is unusual, perhaps mentally ill, maybe with a bipolar or borderline disorder, but diagnosis is not really the point. She is warm, spontaneous, beautiful, and an affectionate if inconsistent mother. Because Mabel is so eccentric and unpredictable, the Longhetti family seems to function at a kind of delicate equilibrium.

This stability is disrupted when Nick fails to get away from work on a night he and Mabel had planned to spend alone together. The children are with her mother, and Mabel finds it intolerable to be alone, so she gets drunk, goes out, and picks up someone in a bar. The next morning Nick brings a crowd of work mates home with him after the night shift and Mabel copes with the invasion by cooking up a spectacular spaghetti breakfast and flirting outrageously with one of Nick's friends.

Later when a neighbour brings his children to play, Mabel again behaves inappropriately. Nick, under pressure from his mother and Mabel's physician, is persuaded to have his wife institutionalized. She is taken away. Nick angrily rejects the concern of his friends, but struggles terribly to manage the children.

The film ends with the evening of Mabel's return from hospital. Nick and his mother have arranged a dinner party to celebrate her recovery, but it is quickly clear that, despite electroconvulsive therapy, Mabel is unchanged. It also becomes more evident than ever that her "madness" is rooted as much in the family's social network, her uncomprehending parents, judgmental mother-in-law, and volatile husband, as it is in her own brain or personality. But, after an appalling evening, Mabel and Nick put the children to bed and then go about cleaning up the house as usual, their fragile normality restored for now.