When the police uncover a narcotics smuggling operation, the driver is shot dead. The man turns out to be Superintendent Martin Beck's son. Beck breaks down and steps away from the investigation but later returns at his colleagues request.

Inspector Beck and his team get involved in a large-scale smuggling of cesium 133. A gang from the east uses refugees who with a promise to stay in Sweden and with danger to their own life take in the dangerous explosive chemical substance.

A homosexual police officer's double life is paid by Beck's archenemy, Gavling, a man who runs Stockholm's underworld. In return, the officer has been providing Gavling with secret information from the police archives.