Police Chief Herville is found dead in a Chinese restaurant in the 13th arrondissement of Paris. Gilou must break the news to Laure, who is being treated in a police rehabilitation centre. Now in charge of the unit, Gilou begins investigating with new recruit Ali, who is fresh out of training.

Meanwhile, Judge Roban returns to work from his time off sick only to find he is soon due to take compulsory retirement. And lawyer Joséphine struggles to adapt to life in prison while awaiting trial.

As the police identify that their top priority is to track down Ryan and his gang, Gilou agrees to work with Laure again, but she must find her place now that he and Ali are a team. Meanwhile, Edelman provides legal counsel to Joséphine to help her get out of prison.

Ryan is not telling the whole story, so Roban decides to lock him up. The banknotes recovered from the robbery lead police to take their investigation to a nearby housing estate. Meanwhile, a link is uncovered between Wang and Herville, and Joséphine builds a rapport with her cellmate, Lola.

Laure follows the drug traffickers’ courier to a warehouse in Aubervilliers, where the investigation suddenly acquires a new dimension. Meanwhile, still frail, she struggles to cope with the responsibilities in her personal life. Joséphine has a hearing with the judge. And Roban pursues a case of negligence at a hospital by involving the hospital director.

Police work to uncover the role of Ryan's elder brother Fouad in the money-laundering scheme. Beckriche calls on his former colleagues at the fraud squad to assist in the investigation, but his decision is controversial. Laure and Gilou make a breakthrough arrest, while Edelman presses for a crime scene reconstruction he thinks will help Joséphine.

The money-laundering operation closes ranks. Beckriche orders his team to let the fraud squad take the lead with their investigation, but will his colleagues comply? Out of prison, Joséphine finds herself trying to pick up the pieces of her personal and professional life.

Following the debacle resulting in Fouad's death, the team is taken off the investigation. Laure is increasingly concerned about Lebrion's interference, while Joséphine realises she also has reasons not to trust Edelman.

Roban falls into a trap set by Joséphine and Edelman, whose professional partnership is now, however, on the rocks. Laure and Gilou continue to work on the investigation they've officially been taken off, identifying a suspect who may have been involved in the money-laundering operation. Beckriche's loyalty to his former boss is put to the test.

With his role in the investigation irreparably tarnished, Roban loses his grip on the case. Laure and Gilou go ever further out on a limb with a rogue decision to reactivate the now-dormant money-laundering operation. Joséphine, who now works for Solignac, continues to set traps.

Laure and Gilou sink deeper into taking illegal measures, risking yet more grave repercussions. Their former team member Tintin is tasked with investigating their methods. Meanwhile, Joséphine does her best to protect Lola. However, she proves to be a most uncooperative defendant - for reasons that Joséphine understands only too well.

When Laure and Gilou, under investigation by Internal Affairs, are taken into custody, Tintin is torn between his loyalties to his former colleagues and his new job. Josephine also faces a moral decision about how best to fight Lola's case.