Dead waters of the Moscow Sea

Afanasy Karachaev was found dead in his apartment. The official conclusion of death indicates heart failure, but Lyalya, who loved Karachev, does not believe this conclusion. She turns to private detective Alexei Kisanov, who takes up the case. Very soon it becomes clear that Karachaev was helped to go to the next world. But this was the first and last clear point in this matter: what follows is complete riddles. The daughter of Afanasy Karachaev disappears in the most mysterious way, and a detective is looking for her traces in the dark waters of the Moscow Sea...