When the charred remains of woman are found, Säpo, the Swedish Security Services, suspect Gunvald Larsson of being mixed up in her murder. The dead woman was wanted internationally and a member of a group of militant eco-activists carrying out attacks around the world. Gunvald sets out on his own to find the woman's murderer, with Säpo on his heels. Martin Beck is ordered to arrest Gunvald and his loyalty to his colleague is now put to the test.

In a playground in the middle of urban idyll found a buried wooden box containing a known and respected prosecutor. Beck & co suspect first a rough criminal MC-leader of the deed, but you can quickly re-evaluate the case when the MC-leader is found murdered in a similar wooden box. Pretty soon discovered a number of wooden boxes and the police realize that you are in a cat and mouse game with a crazy serial killer.