A newly-married woman becomes frustrated as her husband, a reindeer herder for an Arctic village, spends much of his time away. Desperate for affection, she visits a shaman who offers a potion that makes her irresistibly desirable, with unexpected and deadly results.
Pekka Puupää and Pätkä, who return to Helsinki from an unsuccessful variety show tour, are forced into refresher training, where they are trained as frogmen. During the diving exercises, the friends encounter the mermaid Helmi, whom they help into the bathtub at home, to Justiina's shock. The friends, who have become civilians, eventually end up on a plane bound for Suez, being cornered by UN soldiers.
The new idealistic welfare officer Helmi tries to improve conditions in "Sin Alley," but difficulties arise, particularly with the leader of the petty criminals, Jukka, whose son Reino also drifts into a life of crime.
