Cold, rain, and fog surround a plant in Ravenna. Factory waste pollutes local lakes; hulking anonymous ships pass or dock and raise quarantine flags. Guiliana, a housewife married to the plant manager, Ugo, is mentally ill, hiding it from her husband as best she can. She meets Zeller, an engineer en route to Patagonia to set up a factory. He pursues her, they join friends for a dinner party of sexual play, then, while Ugo is away on business, she fears that her son has polio. When she discovers the boy is faking, she goes to Zeller, panicked that no one needs her. He takes advantage of her distress, and she is again alone and ill.

Ugo, an electronics engineer, his neglected young wife, Giuliana, and their 5-year-old son, Valerio, live in industrialized Ravenna. Corrado, a mining engineer, arrives from London to recruit skilled workers. He meets Giuliana, and the two are immediately attracted to each other. Corrado learns from Ugo that Giuliana is suffering from nightmares and depression as a result of shock from an automobile accident, but he soon realizes that her mental condition is much worse and that she had tried to commit suicide. When Ugo goes away on a business trip, Valerio pretends to be paralyzed, a trick which badly frightens his mother. Upon learning of the deception, Giuliana angrily leaves him and goes to Corrado's hotel room. She compels the reluctant man to make love to her, but she realizes that the affair will not "cure" her. Wandering aboard a ship, she and a Turkish sailor have an uncommunicative sexual encounter. The next morning, she and her son walk calmly by Ugo's factory where yellow smoke pours from the chimney; Giuliana explains to Valerio that the poisonous smoke does not kill the birds, because they have learned to fly around it.