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.
A group of young robbers, specializing in robbing shopping center security guards, are raging through out Gothenburg. A robbery goes awry when an innocent passerby is killed. Ricky, the gang's young leader, tries to quickly find an expert who can clean the money of the dye pack that exploded while Johan Falk, and his colleagues at GSI, accelerate their hunt.
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.
GSI second in command, Sophie Nordh, flips gangster leader Seth Rydell and convinces him to infiltrate a rogue military group. For the first time GSI Chief Patrick Agrell realizes that he is using a ruthless psychopath as an infiltrator. Can Seth be trusted or does he have his own agenda?
It's a beautiful day in Slottsskogen, Gothenburg idyllic city park, when suddenly the unthinkable happens - gunfire amidst all people. Two gangsters shooting game against each other and a large police operation starts. The conflict grows rapidly to involve several gangs from Gothenburg underworld. GSI switched to try to identify a new thread which proves to be both larger and better armed than any other. The only clue is a tattoo on one of the killed gang members.
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 is a two-fisted Gothenburg cop who finds himself in a shoot-out with jewel robbers. After the smoke has cleared, one robber, shot by his accomplice, and an innocent bystander, are dead. Three witnesses, including Helen, identify thug extraordinaire Leo Gaut as being the dead crook's trigger-happy colleague. Gaut soon threatens the three witnesses, and only Johan, the badge-wearing hero, can save them.
A car explodes in front of a primary school where GSI boss Patrick Agrell has just left his children. The event reunites Johan Falk with Leo Gaut, a former criminal restaurant owner who Johan put behind bars a decade ago.
John Falk is on a routine mission with the Gothenburg police special unit GSI. With the help of a Norwegian undercover police and a civilian infiltrator in one of Gothenburg's heaviest criminal gangs, the GSI are trying buy six assault rifles and thus get them off the street. But suddenly everything changes when a new unknown player suddenly and immediately wants to buy not only those weapons but even more, including armor-piercing shells. GSI realizes that this can not be any ordinary robbers. Someone will start a war on the streets of Gothenburg. At the same time as the situation gets more and more complicated for John Falk's infiltrator Frank Wagner when the leader of the gang he infiltrated realize that one of his own leaking to the police.
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.
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.
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 ...
