Childless spouses writer Andrei and artist Olga adopt the eight-year-old Ksyusha. The director of the orphanage where the girl was brought up is Andrei Iren's ex-girlfriend. She still passionately loves Andrei and intends to return him at all costs, even if for this he will have to destroy his family happiness. Meanwhile, Andrei is writing a science fiction novel about the dark side of Petersburg. On the pages of his book, the city on the Neva turns into a phantasmagoric world, where time itself has stopped, and the streets are inhabited by soulless creatures. Suddenly, Ksenia enters the world of "dark Petersburg" from the novel by Andrey, where he meets a mysterious friend Paramon. Heroes are waiting for many dangerous adventures...