Three bank robbers kill a guard in a heist and flee with the loot. Looking for a place to hole up, they find an isolated hut among the Iberá wetlands, on the banks of the Paraná River. The precarious house is inhabited by an elderly trapper, hermit and eccentric. The fugitives take over the hut and decide to remain hidden there for some time. Days go by slowly. Boredom, inactivity, and lack of women make the fugitives restless and irritable. One evening, one of them, Roberto, wandering around, bumps into a beautiful girl, with blond hair and very pale skin, bathing naked in the river. When he tries to get closer and start a conversation, she turns away from him and loses herself in the bush. Is she real or was it just a mirage? Upon returning to the hut, Roberto recounts what happened to his two henchmen. The old trapper then tells them the strange, tragic story of "the Irupé flower", a legend that has been circulating in the area for some years. She is a female spectrum, a beautiful girl who can be seen bathing naked in the waters of the river, on nights of full moon. According to legend, the young woman, the only daughter of a local aristocratic family, was found dead in those waters after a horrible tragedy. During her honeymoon, an insane gardener attacked her new husband and killed him, then raped the young wife. Mad with pain, the girl ran towards the estuaries, entering the waters, where she found her death. Since that tragic day, the ghost of the beautiful young woman returns every full moon, hoping to reunite with her dead husband. Although it is a disturbing story, the criminals do not believe it. But a few days later, Roberto meets the girl again. Her name is Marta and she turns out to be flesh and blood. Right there, the man and the woman make love, and soon fall in love. But things will not be so easy for Roberto and Marta, "the Irupé flower".