The 1st of September starts with a tragedy for 11-grade pupils of an ordinary school when Polina Dudka, an honor student and school's pride, is found dead. Olga Makarova, an investigator whose son is Polina's classmate, tries to discover whether the girl committed suicide or if she was intentionally pushed down the roof.

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During her investigation, Makarova discovers scary secrets hidden by the pupils, their parents and even her son. Polina's death is just the starting point in a cascade of terrible events.