Uuno Turhapuro armeijan leivissä

Uuno is forced to return to the army because it was discovered he only served one single day as a young man. Finnish law requires mandatory military service, and when the authorities realized he had not completed his conscription, he was recalled to finish what he started.

The army leadership suspects Uuno has been sent by his father-in-law Councillor Tuura, who just became Defence Minister, to expose flaws in the army's leadership and conduct. They misinterpret his presence as a covert mission rather than simple conscription, so they try to bribe him with promotions to keep him quiet.

Earlier, the officers note Tuura's sudden political elevation, which triggers their suspicion.

Uuno is promoted from private to major within a single week because the army officers keep offering him promotions in exchange for his silence about their perceived shortcomings. Each promotion is an attempt to appease him and prevent him from reporting their failures to his father-in-law the Minister. Uuno remains completely unaware of the political maneuvering happening around him.

Elisabeth Turhapuro impersonates Uuno to buy him time when an urgent meeting at a restaurant comes up. She steps into his place hoping to handle the situation while he deals with other matters, unaware that her impersonation will lead to further complications including a detour through the woods and a malfunctioning radio.

During the chaos of Elisabeth's impersonation day, she ends up in the woods with a malfunctioning radio. Meanwhile, Tuura picks up the confused radio signals and, in a moment of mishap while trying to communicate, accidentally issues a declaration of war against Sweden. The faulty communication equipment and misunderstanding lead to the official crisis.

The defective radio first appears during Elisabeth's chaotic day in the woods.

Tuura is court-martialed for accidentally declaring war on Sweden. Despite the declaration being a mistake caused by faulty radio equipment and miscommunication, the military treats it as an official act requiring accountability. The proceedings become a farcical legal proceeding rather than a serious trial, consistent with the film's tone.

Uuno takes on the role of Tuura's defense attorney at the court-martial because Tuura is his father-in-law and family loyalty compels him to help. Despite having no legal experience, Uuno's bumbling yet earnest efforts turn the serious military proceedings into a showcase of his characteristic wit and improvised chaos.

Uuno's old friends Härski Hartikainen and Sörsselssön return to the army for refresher courses, essentially rejoining military service. Their return brings back the classic slapstick chemistry that defined the earlier Turhapuro films, and their presence amplifies the comic chaos surrounding Uuno's unusual military experience.