Hapless swindler Gosha steals Guarneri's violin, but the accomplice substitutes him and takes the valuable instrument for himself. Gosha falls into the hands of law enforcement officers and becomes the main suspect. The junior investigator Vera, who was demoted to assistant under Lieutenant Colonel Guzin, is entrusted to conduct this case. But here's the catch: after a quarrel with the boss, the girl is fired, and soon Gosha's accomplice, the Scarab, is found dead.

Gosha understands that the only way to prove his innocence is to surrender and side with the investigation. So a loser thiefand the former investigator, eager to annoy former colleagues, decide to conduct their own investigation by organizing the Alibi detective agency. Now they have one "Alibi" for two!