Wunderkinds Also Cry

A rare flute has been stolen from the house of a very wealthy man. The circumstances of the case are such that investigator Colonel Berg seeks help from Denis, Kolya, and Katya. The circle of suspects is small, but each... has a motive and the opportunity to commit the theft. How to identify the criminal?
While the detectives are conducting an undercover investigation, something mysterious is happening in the house: something heavy falls in the middle of the night -- even the walls tremble, a shadow silently glides up the stairs, and at another time a shadow, hunched over three times, drags something somewhere… And how to explain that the French teacher suddenly stops understanding French, and the same person is at the same time in completely different places?...