A famous industrialist is murdered at a restaurant in Malmoe. Police inspector Martin Beck in Stockholm gets the case. The suspects lead to people involved in illegal arms deals. But who was the biggest criminal, the murderer or the industrialist?

The city of Mahagonny, founded by three criminals, becomes a place for people looking for their luck or money. One among them is the lumberjack Jim Mahoney. However, he is disappointed by what the city is.