Pekka ja Pätkä sammakkomiehinä

After their failed variety-show tour, Pekka and Pätkä receive a military summons for refresher training. Since they are both able-bodied men, they are enrolled in a frogman (underwater combat) course, which becomes the next chapter in their unpredictable journey from civilian performers to accidental soldiers.

While practicing diving exercises in the outer archipelago, Pekka and Pätkä discover a mermaid named Helmi. Instead of leaving her in the ocean, they bring her along and place her in their bathtub at home, treating her as a curious addition to their routine rather than a wild creature.

When Justiina Puupää finds the shimmering creature in the bathtub, she has never seen a mermaid before. The unidentified aquatic animal appears as a large fish to her untrained eye, so she assumes it must be a giant pike, which is a common freshwater fish in Finland.

While relaxing on a park bench, two departing UN peacekeepers knock Pekka and Pätkä unconscious and exchange their civilian clothes for UN peacekeeping uniforms. This identity swap accidentally enrolls them in a Finnish UN peacekeeping mission to Suez, as they wake up believing they are still themselves but are actually heading to a war zone.

After the uniform switch, Pekka and Pätkä are taken to Helsinki-Vantaa Airport under the assumption they are the replacement peacekeepers. The plane delivers them to a Finnish UN peacekeeping camp near Suez, Egypt, where they arrive expecting routine duties but find themselves in an unexpected international situation.

The newspaper they were reading on the park bench hints at the ongoing UN operations that will later sweep them into the mission.

After being discovered in the bathtub and causing household chaos, Helmi the mermaid is brought to Linnanmäki amusement park, where she becomes an attraction called the 'water maiden.' The whimsical setting provides a perfect home for the magical creature while adding a surreal element to the film's comedy.

The boxing match between navy and army personnel serves as comic relief and showcases the playful rivalry between military branches. It underscores the film's theme of competition and camaraderie while providing lighthearted entertainment amid the duo's increasingly absurd adventures.

Pekka and Pätkä successfully complete their frogman refresher training and are officially discharged with thanks. The military releases them back to civilian life, but their return to normalcy is short-lived since the UN uniform incident happens immediately afterward.

When Pekka and Pätkä discover Helmi during their diving exercises, they see her as an opportunity to add excitement and novelty to their performances. Their mentality as struggling entertainers drives them to treat the mermaid as a potential attraction rather than leave her in her natural habitat.