During the autumn of 1970, in one of the Central Asian Soviet Republics, three criminals pull off a daring theft: they steal Alexander the Great’s golden helmet from an archaeological excavation. The crooks are led by Aleksandr Belyi (Evgeny Leonov), a ruthless big-shot, flanked by his two henchmen Fyodor Yermakov, known as Crosseyes (Savely Kramarov), and Gavrila Sheremetyev, nicknamed Sad Sack (Georgiy Vitsin). In Moscow, Professor Maltsev, who heads the expedition, meets a man who looks exactly like Docent and discovers that the lookalike is Yevgeny Troshkin, an amiable principal of Kindergarten No. 83 (also played by Evgeny Leonov).
The mix-up seems tamed, but soon the police realize they’ve already captured the trio while the helmet remains missing. They enlist Troshkin to pose as Docent to uncover where the helmet is hidden. Troshkin is dressed in a disguise with a toupee and fake tattoos and sent to a Central Asian prison where Docent’s accomplices are serving time, while their boss is kept near Moscow. To pull off the deception, Troshkin—an educated and good-natured man—must learn the criminals’ slang and mannerisms.
He passes as Docent and feeds Crosseyes and Sad Sack a fake alibi, under which he pretends to have lost his memory about the helmet’s whereabouts. Yet the criminals know little about Docent’s network and cannot name the place they last saw the helmet. The police stage a mock escape for the trio, hoping Troshkin can coax them back to Moscow to continue the search.
The trio are supposed to squeeze into an empty cement truck, but end up in the wrong vehicle, their clothes caked in cement, forcing them to run in their underwear into a nearby town and pose as a track team. A local petty crook, Vasiliy Alibabaevich Alibaba (Vasiliy Alibabaevich Alibaba), joins them after escaping in the confusion, and he stays along because the danger of exposure looms. Radner Muratov brings this character to life as the reluctant ally who wants to do the right thing but is trapped in a risky game.
In the town, the group holes up in a hotel. A botched chess game leads to a fight between Crosseyes and Sad Sack, which Troshkin breaks up and then orders the pair to drop their criminal slang and act like ordinary people to stay out of trouble. To earn money and keep up appearances, Troshkin takes a job at a local kindergarten, carefully arranging situations so his companions won’t suspect anything while he buys new clothes and a place to stay. Alibabaevich feels remorse and even contemplates surrender, but fears a harsh punishment.
After a stint in Moscow, the gang moves into an old house slated for demolition while Troshkin and the others roam the city looking for clues. Alibabaevich guards their hideout, and tensions rise when Sad Sack steals Troshkin’s money. A fire accidentally started by Alibabaevich drives the criminals to relocate again, this time to Maltsev’s country house. Lyudmila, Maltsev’s daughter, arrives believing they are archaeologists, and her presence adds a new dynamic to the quietly tightening web of identities.
As Troshkin traces Docent’s network, one former accomplice quits crime and confronts Troshkin, sending him tumbling down a staircase. Another ally, Prokhorov the cloakroom attendant, also tries to arrange a meeting near the Bolshoi Theatre. Prokhorov’s associates become convinced that Troshkin isn’t Docent and assume he’s an undercover cop, prompting Prokhorov to disappear to avoid trouble.
Police brief Troshkin that the real Docent has broken out of his prison near Moscow and may head toward his old gang, making the operation urgent. Troshkin requests permission to stay with the crew to see New Year’s celebrations through, hoping to awaken their consciences and plead for a change of heart, even if it means continuing the masquerade. At Maltsev’s country house, Troshkin delivers a speech meant to lift the group’s spirits, but the criminals only view it as another cover for crime and reject Docent’s past violence.
Meanwhile, the real Docent arrives at Mityai’s apartment, where he meets Prokhorov. Both think he’s either the same fake Docent or a police observer, and Docent asks for a hideout. In a tense rooftop confrontation, Mityai tries to trap Docent, but Docent overpowers him. Prokhorov draws a gun, which Docent later appears to wield with surprising skill, turning the tables.
Back at the country house, Troshkin tries to give the gang gifts and also shares a letter from his relatives that he received through the police. The criminals grow increasingly agitated by Docent’s oversight, seeing only a longer path to prison if they stay in crime. Sad Sack, moved by a sense of guilt and the looming danger, attempts suicide but fails. The gang, fearing further trouble, decides to surrender to the authorities.
Troshkin, unhappy with his masquerade, attempts to reveal himself, but the others bind and gag him. Crosseyes recounts a painful memory of Docent forcing him to dive into an ice-cold hole, and Sad Sack realizes the helmet is hidden in the lake. They rush to the local boat station, where the real Docent confronts them, knife in hand. He orders Crosseyes to recover the helmet from the ice, retrieves it himself, and departs, leaving the gang to deal with the naked Crosseyes.
Lyudmila’s timely arrival at the country house adds another layer of tension as Troshkin, now bare-faced and unmasked, faces the two Docents. A brief clash ensues in which Crosseyes, Sad Sack, and Alibabaevich subdue both Docents with an oar and decide to turn them over to the police, thinking that two Docents would only increase their potential prison time.
In the end, the police take both Docents away, and Professor Maltsev finally recovers his helmet. The criminals stand perplexed as the police question why they aren’t being taken away as well. Then a vehicle stops, and Troshkin emerges, having discarded the wig. Seeing this, the trio bolts away in fear, while Troshkin chases after them to bid farewell—his mission complete, even as the line between disguise and truth remains thin.
