After his car blew up, Theo was taken to hospital in a critical state. Caplan and Morlighem go to Vogel's place, determined to avenge their companion. Vogel finds an ally in the shape of Oriane Béridzé, who also wants to eliminate Caplan. Her plan is to force her father, an ex-cop, to contact Caplan and put him on the tail of a trafficking network run by the Russian mafia. An ambush. Meanwhile, Roxane is deeply upset about Theo, and watches over him day and night.
Caplan and Morlighem have intercepted a truck from a company owned by the Russians. Then they discover a vast prostitution network. Georgian mafia expert Andrew Megrelishvili tells them that there's a threat of a war between rival gangs.
With the death of Vissarionovitch - who ruled as "boss of bosses" over several Russian-speaking mafia clans - a bloody war of succession is shaping up between the two pretenders: Jordania and Pavlovitch. Roxane continues to operate alone, tracking down Vogel's sister thanks to information provided by Vanderbeke. In the meantime, Caplan, Morlighem and Megrelishvili stake out the funeral where Vissiniarovitch's burial service is due to take place. Odessa, a female contract killer, sets up shop in a hotel opposite, ready to strike.
After an assassination attempt, Jordania is placed under police surveillance in hospital. His adversary, Pavlovitch, teams up with Atom Parajdanov. They are trying to get to Jordania any way they can. Caplan offers him a deal: hand over information on his rivals (become a "STOUKATCH" - a traitor) in exchange for police protection. Meanwhile, Vogel and Oriane take Hélène Rossi hostage to put pressure on Caplan.
Oriane has managed to work her way into Caplan's group as an interpreter. She is bent on vengeance. Caplan has his gun in his hand when the Russians launch an assault on their stakeout. Flashback: five years earlier. A war within police ranks between Rossi/Caplan's unit and Vibert's. During an operation, Vibert shoots a suspect in cold blood. Turned in by Caplan, Vibert is sent to prison. Oriane, who is in fact Vibert's daughter, has been seeking to avenge her father ever since.
The Russians got the better of Jordania, who was killed in the course of the attack. But how did the maximum security safe house get located so quickly? Caplan's suspicions fall on Andréas. Under questioning, Andréas explains that he is working to a plan drawn up by Georgian police in agreement with their French counterparts, the aim of which is to lure the top boss of the Vor V Zakone from Moscow and to arrest him in France. And Caplan's unit had better keep out of their way.