Marta has a sexual relationship with her stepfather and they have a son together. Her mother suspects that her husband fathered the baby, but she is mentally ill, and everyone is willing to pretend that her accusations are baseless. Marta learns that her stepfather/baby daddy plans to abandon his family and decides to murder him, taking advantage of her mother's psychiatric condition to blame her for the murder. DNA proves paternity, giving police the break in the case.