Carloni, Gino Rossi works at a Milan detective agency, tracing photographs of Paola Molon Fontana, Lucia Bos, a woman married seven years earlier to the wealthy industrialist Enrico Fontana, [Ferdinando Sarmi]. Fontana’s recent discovery of these old pictures unsettles him, and he hires Carloni to uncover whatever he can about Paola’s life before the marriage. Carloni travels to Ferrara, a city steeped in memories for Paola, where he learns she was best friends with two local girls. He visits the apartment of one friend, Matilde, and hears from Matilde’s husband that Matilde’s friend Giovanna Carlini died in a tragic elevator shaft fall just days before her wedding to Guido Garroni, a local boy with whom Paola had also been involved. When the sullen Matilde arrives home, she refuses to cooperate with Carloni. After the detective leaves, Matilde writes a letter to Guido, alerting him that a suspicious man is probing Paola’s past.
Back in Milan, as Paola exits the La Scala opera house dressed in a white fur coat with her husband and friends, she is startled to see Guido across the street. Later that night, she receives a phone call from him and they agree to meet the following day. At Idroscalo lake, Guido, who is now a struggling car dealer, shares Matilde’s letter with Paola. The thought that someone is digging into their past frightens Paola, making her worry that Matilde might be attempting to extort money. With their former attraction rekindled, the two agree to meet again. Meanwhile, Carloni’s investigation intensifies as he uncovers more about the mysterious accident in the elevator shaft, Paola’s sudden disappearance, and Guido’s role in all this. He learns from Giovanna’s maid that Paola and Guido were with Giovanna when she fell to her death, and that they did not cry out or rush to her side. He also learns that Paola left Ferrara two days after the accident and met her future husband shortly thereafter in Milan—never telling him about Giovanna’s death.
In the days that follow, Paola and Guido’s once-casual reunion escalates into a full-blown affair played out in rented rooms. To help Guido earn money, Paola arranges for him to be the middleman in a car sale that doesn’t work out. As their relationship grows, Paola’s frustration with her loveless marriage leads her to suggest to Guido that her husband’s death could benefit them both. At first Guido is repulsed by the idea, but Paola’s emotional manipulation slowly sways him. Later they meet on a bridge over a desolate canal that Fontana traverses on his way home. Guido plans to shoot him as he approaches the bridge. Paola pretends to have second thoughts, accusing Guido of being responsible for Giovanna’s death—he saw the elevator door open and did not warn her. Guido reminds her that she too did nothing to warn her friend, and that they will both be responsible for this death as well.
Pressured to finish his report, Carloni writes of the affair and the suspicious circumstances surrounding Giovanna’s death, and submits the document to Fontana. Upset by the revelation, Fontana gets in his car and drives home along the canal road, where Guido is waiting. As the car nears the bridge, Guido hears the sound of a distant crash and rides away on his bicycle toward the scene, where Fontana’s overturned car is engulfed in flames. Fontana’s dead body lies nearby, and police begin their inquiry.
Soon after, as Paola’s household is informed of the accident, she runs off, fearing arrest. She reunites with Guido, who reveals that Paola’s husband is dead and that he was not involved in the event. After Paola declares her love for Guido, he agrees to meet her the following day. As Guido steps into a taxi, he asks to be taken to the train station.
