A tumultuous and often violent love story transpires between Mathieu, a wealthy middle-aged Frenchman portrayed by Fernando Rey, and Conchita, a beautiful yet impoverished flamenco dancer from Seville, played separately by Carole Bouquet and Ángela Molina. Their contrasting appearances and temperaments add to the chaotic nature of their relationship, which unfolds mainly through flashbacks as recalled by Mathieu.
The film opens with Mathieu on a train journey from Seville to Paris, attempting to escape the clutches of his youthful girlfriend Conchita. As the train is about to leave, he spots a disheveled and injured Conchita chasing after him. In a desperate attempt to deter her, he splashes a bucket of water over her, but rather than backing off, she climbs aboard the train.
Inside the train, other travelers, including a mother with her daughter, a judge who knows Mathieu's cousin, and a dwarf psychologist, witness Mathieu’s brusque behavior and question his motives. This initiates a recounting of his contentious relationship with Conchita, set against the tumultuous backdrop of violent political upheaval and bombings by leftist factions.
Conchita, who claims to be 18 yet seems more mature, pledges to remain a virgin until marriage, teasing Mathieu with sexual promises while denying him satisfaction. One memorable scene involves her wearing a tightly laced corset, making physical intimacy impossible. In another twist, Mathieu discovers her concealing a young man in her apartment, leading to a cycle of breakups and reconciliations that leave him frustrated and bewildered.
Eventually, Mathieu stumbles upon Conchita performing nude for tourists in a Seville nightclub. Initially consumed by fury, he ultimately forgives her, even purchasing a house for her. However, in a heart-wrenching moment, after moving into the new home, Conchita bars him from entering, expressing her disdain for him and suggesting that his mere presence disgusts her. She provocatively appears to engage in sexual relations with another man in front of him, yet he chooses to walk away without witnessing the act.
Their saga takes a darker turn when Mathieu is confronted and held at gunpoint during a carjacking later that night. In a twist of fate, Conchita seeks to make amends, claiming her earlier sexual encounter was a ruse and her supposed lover is actually a gay friend. However, her explanation leads to a violent confrontation where Mathieu strikes her, resulting in the bruised and bandaged appearance established earlier in the film.
As the train passengers seem satisfied with Mathieu's narrative, Conchita surprises him by dousing him with water once again. Despite their tumultuous exchanges, they appear to reconcile for a final moment as they disembark the train and stroll through the streets of Madrid, arm in arm, seemingly relishing their reunion.
The story culminates in a vividly chaotic atmosphere in a Paris shopping mall where loudspeakers announce an impending wave of terror orchestrated by extremist factions. As bomb threats loom and political tensions mount, the couple's argument coincides with a catastrophic explosion, leaving their fates hanging in the balance as chaos ensues around them.
