Larsson and Kollberg are extremely reluctantly part of a special task force that needs to solve a spree of bank robberies.

Martin Beck is given a pity job after recovering from being shot at the conclusion of The Abominable Man; he needs to solve a classic situation of the genre: the locked room mystery.

At the same time Martin Beck solves the locked room mystery- the gun was shot from outside by Maurtizon, when the window was open.

During the investigation, Beck, in a depressive phase of his life, meets a woman named Rhea Nielsen and he finds new courage which in the following novels plays an important role.

Criminal mastermind Werner Roos and bank robbers Malmström and Mohrén are introduced, as is their ineffectual but successful Nemesis, public prosecutor 'Bulldozer' Olsson.