Yes, the detective office “Quartet” has never investigated anything like this before! Asya and Mathilda’s classmate, Lyudka Kosheleva, has… a real father showing up—one who once abandoned their family. Here you’d think there’s something to celebrate, but Lyuda somehow feels that this person is lying to her for a reason, and that he’s not her father at all! But how can she prove it? She can’t bring herself to ask her mother. And there’s nothing left to do except turn to professionals for help—Asya and Mathilda—because the whole school has long known that, together with their friends Kostya and Mitya, they have solved more than one difficult case. The young detectives couldn’t refuse their school friend. And so the operation plan “Fake Daddy” is already ready!..