Verónica León is a homicide inspector in Madrid. For a couple of years now she has been involved in a difficult relationship with sub inspector Roberto Vidal, who separated from his wife at that point. During one of their occasional trysts, they are informed that an old man has been murdered. When they get to the scene, suspicion falls on the widow due to her attitude, although they find certain elements that just don't fit. A second victim appears the next day: a middle-aged woman who has been hung from her window by a rope around her neck, making it look like suicide. Although there is seemingly no link to the first victim, the pair find details that make them think the two crimes are related. With the help of Daniel Harmon, a behavioural analyst who has come to advise them, they are plunged into a race against time.