Falk is blackmailed into smuggling a truckload of guns from Latvia.

Five men break into Frank Wagner's apartment. Frank is able to escape and seeks out the help of Johan Falk. Has someone leaked that Frank is working with the police? Frank and John don't know who knows what and whom to trust.

The police station is locked down. A snitch is compromised. Drastic and unexpected events take place. Both inside and outside the police station.

It's been two years since John Falk and Frank Wagner broke their cooperation and Frank started working undercover with the police. Frank's search for Kevin crosses Johan's investigation and opens up a new collaboration between them - with the big difference that this time it's personal for Frank.

Johan Falk's stepdaughter Nina has gotten in contact with her biological father, Orjan, discovering that he is in debt to an Estonian construction company in Gothenburg, leading to Nina's kidnapping.

The unknown, large mafia organization is now showing its true face. The pressure that GSI and John Falk and his family have put on the organization, makes them fight back on all fronts. The rule book is thrown out. But to go after Johan Falk's family and trying to kill his wife could be the biggest mistake the organization has ever made. GSI closes up around Johan's family and the final battle begins ...

GSI follow up a weapon trail that leads right into Kavkaz mafia headquarters on the west coast. GSI member Niklas Saxlid is the one in the group who is specialized in undercover operations, and he has penetrated Kavkaz' activities. But suddenly something happens and Niklas disappears.

When Johan and his colleagues are watching Seth and his gang member Jack, they stumble on a larger case than they expected. Seth is selling arms to terrorists, but without Jack's knowledge, in a car where Johan's old colleague Pernilla mysterious appears. While Johan begin researching what Pernilla and SÄPO is doing, Jack suspects that everything is not right with Seth and that he's working with the police.

An elderly woman dies in a hospital in Stockholm and it turns out that she suffered from an incurable disease. Her son refuses to believe that it was the disease that was the primary cause of her death.