Mercedes is a stay-at-home girl, conservative and lacking close friends. Her sister Olga, on the other hand, works, is successful and full of vitality. But this annoys Mercedes. She also thinks that their mother has a preference for Olga, but what fills her with envy is that Olga is about to marry the love of her life, Daniel. The only one in the family that seems to care about her is her father. As time passes and the wedding dateapproaches, Mercedes starts to take refuge in religion, deciding she wants to keep her virginity for life as a sign of respect for God. Her parents do not understand her and suggest going to a psychologist. Mercedes becomes tired that no-one takes her seriously and starts going crazy. A few days before the wedding, in a fight for the toilet, Olga returned to mock her, which pushes Mercedes over the edge; she decides to end the life of her sister, drowning her in the bathtub.
