A mentally ill patient escapes from a psychiatric hospital and wanders the outskirts of Madrid. He is driven by nothing more than a desire to kill. After murdering two girls by a river, he begins a series of increasingly gruesome murders, spreading fear throughout the area. Meanwhile, José and Antonio, two close friends, are planning a relaxing weekend at José's family estate outside the city. They invite two sisters, Anne and Laura, who accept. Anne is a composed secretary who is fond of Antonio. Laura, however, is shy and withdrawn following a recent heartbreak. Everything appears set for a pleasant weekend for both couples.