The boss of a black market ring (known only as "The Chief") wants to smuggle a batch of jewelry from a foreign state into the Soviet Union by hiding it inside the orthopedic cast of a courier. The Chief sends a minor henchman named Gennadiy 'Gesha' Kozodoyev (played by Mironov) to serve as the courier. Kozodoyev travels to Turkey via a tourist cruise ship. The local co-conspirators do not know what the courier looks like; they only know that he is supposed to say a code word to identify himself. Due to a mix-up, they mistake Kozodoyev's fellow passenger from the cruise ship, the "ordinary Soviet citizen" Semyon Gorbunkov (played by Nikulin) for the courier. They place a cast around his arm and put the contraband jewels inside the cast. Upon the cruise ship's return to the Soviet Union, Gorbunkov lets the police know what happened, and the police captain, who is working undercover as a taxi driver, uses Gorbunkov as bait to catch the criminals. Gesha and Lyolik (another of Chief's henchmen, played by Papanov) attempt to lure Gorbunkov into situations where they can quietly, without a wet job, remove the cast and reclaim the contraband jewels.