Maria and Andrey Bystrov are investigators of the Investigative Committee. After learning that her husband cheated on her, Maria meets with a former admirer to spite him. Soon she realizes that she is pregnant. The Bystrovs' marriage is collapsing, but they have to conduct a new investigation together. A businessman was poisoned. The poison was in a cake that his wife Elena brought him from work: she explains that the dessert was left to her as a gift by one of the patients. The suspect is quickly located. But when the case seems solved, a new drama occurs in Elena's life. It becomes clear that she has a secret enemy who has come up with a sophisticated revenge plan. But Elena can't remember who she crossed the road to.