A rich widow is found dead in her apartment in Helsinki due to gas poisoning. The incident is initially thought to be an accident, but inspector Palmu notices that the murderer made a mistake, and so Palmu, Kokki and Virta begin the investigation: who had come to the apartment through the balcony door and opened the gas tap while Mrs. Skrof was asleep?
Two upstart families compete while trying to overcome the generation cap with their children.
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.
