Master detective Evert Backstrom is in peak form. He is still making tabloid headlines with his ability to solve murders quickly and efficiently - and arrogantly. But when his rival, celebrity lawyer Tomas Eriksson, is murdered, it proves difficult not to let emotions interfere in the investigation. The evidence points in multiple directions, and before long, more dead bodies are found. The motive connecting the murders seems to be an old music box...

Peter and Barbro tail police commissioner Ludvig Larsson and discover something shocking. Caijsa and Jorma try to find out why Conny had the old case files and realize that one of them is missing: the investigation into Urban's suicide. Stella meets the young girl who sought her help, but when Stella tells the girl she should talk to the police, the girl runs away.

Peter Wendel's Cold Case Unit is understaffed. Jorma quit, Caijsa is on her way to an extended leave, and Peter himself isn't doing well after accepting his brother's suicide. But everything changes when a colleague, Conny, is murdered. In the man's apartment the police come upon old, unsolved murder investigations. Peter and his team are tasked with finding out why he had them.