Former primary school teacher Ksenia Malykhina has disappeared. Her son filed a complaint with the police. Operational officers Captain Timur Ovchinnikov and his partner Vasily Kireev decided to inspect the apartment of the missing woman, in which she lived alone, and at the same time interview the neighbors. The teacher's neighbor, having examined the apartment, did not notice anything unusual. She was about to leave when she accidentally looked into the bathroom and screamed. The bathtub was completely black, without the slightest sign of enamel. The operatives set up an ambush in the apartment. At night they heard someone open the front door...