Armando Andreoli, a well-known engineer approaching eighty, accidentally crosses the path of Federica, a young and attractive nurse. From that moment, a melancholic falling in love on the part of the girl ensues, while the elderly Armando remains trapped in this unexpected passion. After a series of surreal and paradoxical encounters, Armando, frightened by Federica's growing obsession and convinced that she is faking it, perhaps in complicity with her fiancé, out of interest in his fortune, decides to break off all relations with her.
However, when Armando realises he has sincerely fallen in love with Federica, he sees her in the church, ready to marry her fiancé Giorgio. Upon returning home, he discovers that his wife has left him, leaving him a letter explaining that she cannot tolerate the fact that he has fallen in love with another woman, and that they both need a pause for reflection.
In this moment of reflection, Armando realises that his wife, despite her humanitarian work in Africa that has estranged her from him, is still in love with him, especially after she confessed to him that he was her one and only true love, surviving a serious African illness.
Years later, Armando makes peace with his wife and, while on a train from Turin to join her, he meets Giorgio, Federica's ex-boyfriend. From Giorgio, Armando learns that Federica had not only left him at the altar years before, but that she had married Giorgio's elderly father. Armando suspects that Federica did this for financial gain, but Giorgio corrects him, stating that her father had always been a penniless person and had worked hard to survive.
Furthermore, Armando learns that Federica and Giorgio have started a new adventure together working as animators on a cruise ship in the Caribbean, a dream Federica had always wanted. This makes Armando realise that Federica's love for him was sincere and that she was attracted to mature men, regardless of their social or economic status. As he gazes at the landscape outside the train window and imagines Federica dancing the tango on board the cruise ship, Armando smiles, aware that he had always been wrong about her intentions, and is pleased that she is finally happy.