A circle of young zoo biologists are shocked by an unexpected incident: on a winter morning, seven animals with a bitten throat were found in a kangaroo enclosure. Along with general indignation, mutual suspicions and accusations appear: after all, someone let stray dogs or maybe even a wolf into the enclosure! And this “someone”, undoubtedly, must be his own person in the zoo. Probably, this case would have remained a secret if Moscow schoolboy and amateur detective Sasha Gubin had not become interested in him...