New Year is approaching! The house smells like a Christmas tree, the pre-holiday bustle is in full swing at school, and the brothers Dimka and Leshka Obolensky are again busy with the investigation. Leshka’s classmate, Marinka Seregina, had her apartment robbed, but only her old doll was missing. And then someone slipped sleeping pills into the school security guard’s tea and locked the door of the assembly hall right during the rehearsal of the play... It seems that all these troubles are happening around Marinka! What does the unknown attacker want? How to stop his plans? The brothers are determined to solve the mystery before the holiday!