Vera Volina, a single mother has a 15-year-old beautiful daughter who has extreme interest for men. Mother is aware of this, so jealous of her young lover Sergey. Sergey constantly arranges cruel jokes and mocks Vera, who is already intimidated and does not believe anyone. At the school where Vera works, someone steals poisons from the educational laboratory in the chemistry classroom. On the same day, Masha was seen at school. Having read the inscription The Third Extra in her photo with Masha and Sergey, made by the hand of her daughter, the woman finally decides to turn to a psychotherapist.