Engrenages - Season 4

A young couple has been spotted carrying the body of a mutilated man into the woods. Captain Laure Berthaud and her team soon discover that the unidentified man has been killed by a home-made bomb. The team is distracted by from their investigation by internal conflict and the appointment of a new commissioner who wants quick results. Josephine Karlsson is being pressured by a dangerous Russian mobster with links to the Kremlin.

Laure and her team are on the trail of Sophie Mazerat, a student whose car has been traced to the dumping of the bomb-damaged body, and arrest her at the university. Karlsson's attempts to have Moussa Kone freed from detention are hindered when Thomas's cell arranges a vicious reprisal attack against the bank which reported him. New boss Herville is making his presence felt in the squad room and nobody is liking his business methods, especially when this leads directly to the squad losing touch with their best lead in this most complicated of cases.

Berthaud and her team visit the scene of the immolation of a Kurdish detainee and spot Sophie Mazeret amongst the demonstrators outside the centre. Sophie escapes, but they arrest Vasseur and suspect his involvement with the terrorists. Josephine Karlsson is asked to warn the squat of an imminent police raid. Pierre Clement is pleased to learn that Judge Roban has returned to the courthouse and asks his advice when testimony against Berthaud leads her to ask for his professional representation.

Berthaud and her team stake out the Turkish restaurant that the Kurdish suicide victim was known to frequent, and uncover what appears to be an organised work crew of illegal immigrants. Judge Roban uncovers more inconsistency in the investigative procedure in the case of a senior colleague. Josephine Karlsson invites Clement to her sister's wedding where she has a major confrontation with a family member.

The autopsy of the Kurd reveals a hidden clue which leads Herville to upgrade the case to the highest priority. Karlsson receives a visit from Special Branch, who attempt to blackmail her into providing information about Thomas Riffaut. Judge Roban continues to investigate the case against his colleague Garnier and finds that he has a very unlikely ally. Gilou is getting in deeper with the sinister Egyptian brothers.

At a top-level police meeting called when a youth is shot dead in a drive-by killing, Herville boasts that his unit is already investigating a gun-running case and will have arrests within 24 hours. Karlsson visits Riffaut's new hideout and overhears the gang planning a kidnapping. Clement is called to a judicial review with Jorkel and the wife of Jorkel's missing business partner. Berthaud asks Judge Roban to take on the gun-running case.

Berthault and her team are frustrated by new custody laws which ensure the presence of a lawyer during interviews. Gilou is given three days to ensure that the Sarahoui's late licence is approved and Roban is warned that Garnier is using underhand tactics to smear him. Meanwhile, Karlsson is pressured by the Special Branch to provide information on the activities of Thomas Riffaut and his gang.

When the police raid the Sarahoui's flat, Gilou takes the opportunity to break into their nightclub and retrieve incriminating evidence against him. Yussuf cracks under pressure and provides the team with the names of a Kurdish family behind weapons found at Cetin's house. Karlsson turns the tables on her Special Branch investigators and Judge Roban manages to make even more enemies within the 'system'.

On learning of Cetin's release from police custody, the Ozbeks suspect him of informing against them and Rodi is ordered to eliminate him, but Rodi's associates have other ideas. Karlsson is called to the police station to answer a traffic offence, but is instead charged with perverting the course of justice. Roban chases a further lead in the case against Garnier, but time is running out as the judicial review into his own professional behaviour draws ever nearer.

An online clue leads the team to the anarchists' squat, but during a raid Thomas Riffaut manages to escape. A plastic bag found at the scene of Cetin's execution provides a vital DNA clue. Judge Roban is given the results of his disciplinary hearing, but vows to carry on. Clement is hounded by an unsavoury associate of his client Jorkel.

Kolabi is taken into custody and confronted with the evidence against him for the murder of Cetin. His sim card reveals further clues linking him to Rodi Ozbek and arms dealing. Riffaut is warned of Kolabi's arrest but is determined to continue with his plan. Karlsson attends court to defend the illegal immigrants who have been victimised by a factory owner and Roban is invited to a mysterious meeting with Prosecutor Machard

Events reach a dramatic conclusion as the net draws in around Thomas Riffaut and his gang, but departmental in-fighting within the police organisation means that very dangerous loose ends remain on the streets of Paris.