Marcos, Simón Andreu, is a powerful Madrid-based businessman with political ambitions. He is married to his wife Amparo Muñoz, who embodies beauty and determination as Diana. Although their life oozes wealth, their marriage remains childless after years of trying. Diana initially considers adopting a Vietnamese orphan, but at the last moment she backs down, insisting on a biological child. Marcos is sterile and has kept this secret from her. When he finally confesses, Diana reveals that she already knew it, having recently consulted a gynecologist who told her that she can conceive.
Unfulfilled in her desire, Diana becomes attracted to Juan, Patxi Andión, a working-class gas-station attendant who has been saving to move into a comfortable apartment with his girlfriend, Charo Yolanda Ríos. They are a month away from getting married. A car oil leak leads to Juan helping her, and a strong sexual attraction grows between them. Eduardo Ricardo Merino has long lusted after Diana, who has consistently dismissed his advances. When Marcos travels abroad on business, Eduardo invites Diana to a nightclub where she and Juan cross paths with Juan and his girlfriend Charo. That night Diana dreams of Juan. The next day, Diana visits Juan at the gas station and they begin to see each other.
Diana and Juan begin a clandestine affair. Juan opens up about his life, but Diana keeps hers a mystery. The differences in experiences and social class quickly become evident between the lovers. Marcos takes some time off from work and travels with Diana to ski on the mountains; Diana cannot keep Juan out of her mind. Charo works as a secretary in a travel agency, and her boss Baena [Alberto Bové] lusts after her, though she puts him in his place.
As the affair deepens, Juan is teased by his young coworker Sebas [Chacho Lage], and rumors threaten to surface. When Diana returns from the mountains, she and Juan are reunited in a hotel room. Juan is deeply in love and hopes for something more lasting, while Diana remains distant and calculating. Baena happens to meet his own mistress in the same hotel that Diana and Juan use for their trysts, and he warns Charo that her boyfriend is having an affair. A confrontation ensues, and Juan and Charo’s engagement is threatened.
Diana discovers she is pregnant and is overjoyed to have achieved her long-held desire. She tells Juan that she is in fact married and carrying his child, but that she has never truly loved him—she used him to conceive. Juan is heartbroken and furious. Diana confesses everything to her bewildered husband. Marcos, concerned about a scandal and his image, coldly accepts the situation and arranges an encounter with Diana and her former lover, offering money to Juan in exchange for his silence. Juan refuses, and the two men end up in a fist fight.
Even as the dust seems to settle, Diana suffers a miscarriage. Juan returns to Charo, who remains deeply in love and forgives his infidelity, and the couple redraws wedding plans. Marcos, sending men to teach Juan a hard lesson, makes sure he forgets the past. In the aftermath, Diana turns her gaze toward a new, younger athlete who has just won a swimming contest, suggesting her restless energy seeks new ambition. Marcos watches from a distance, quietly validating the next chapter of his wife's life.
