Carin receives a mysterious letter and decides to investigate a case outside her jurisdiction, while Ingrid challenges troubling conduct at the station.

An abrupt exit casts doubt on the experiment's future. A surprise guest arrives for Carin, and a powerful external force pulls strings behind the scenes.

The women start finding their feet, with Siv earning respect for an arrest and Carin determined to uncover the truth, but Ingrid's conscience irks her.

Carin opens up to Siv and Ingrid and tries to make up with Arne. The case deepens as investigators interrogate a dangerous figure and secrets unravel.

As the final evaluation looms and the experiment's future is on the line, Carin must make a difficult decision that will impact the case — and her peers.