Debailly is prisoner of IS in Iraq. DGSE asks Nadia to negotiate his release through an intermediary Shahanah, a corrupt art dealer, and promises her an EU Deputy Commissioner position in return for her help. Sisteron is sent to Iraq to meet Kurdish fighters and rescue him, but their attempt to do so during a sandstorm fails. He finds an SNCF railway points diagram left behind by IS, which DGSE believes is an attempt by 'Cochise', someone senior within IS, to communicate with them. Meanwhile Marina is working as a seismologist and is still traumatised by her experiences in Iran.

One of Debailly's jailers is a Russian FSB mole and offers to help him. Meanwhile, Duflot tries to help Marina overcome her trauma. Shahanah takes Nadia to meet Lely, a female intermediary for IS. Sisteron and Kurdish fighter Esrin are ambushed by snipers and she is injured, and flown to France for treatment. Sisteron suggests to Duflot that Esrin should be recruited in exchange for help with her son's education. Marina, plagued by panic attacks, resigns from the DGSE. The FSB mole is seriously injured in combat.

Debailly loses hope after his FSB helper is wounded, and stops eating. Marina is approached by Phillipe, a Mossad agent who is posing as DGSE and wanting to recruit her. DGSE advises her to accept the offer, and report everything back to them. Shahanah requires Nadia to launder stolen artefacts from Syria in return for his help with the negotiations, but she refuses to compromise herself. The FSB mole recovers in hospital, and returns just as Debailly is being filmed for a new hostage video by IS.

The CIA wants to bomb the camp where Debailly might be held, but DGSE insists they wait. Duflot wants to get Debailly released before he retires, but MAG reminds him that the agency doesn't normally make much effort to rescue disloyal agents. DGSE use Prune to pressure Nadia into agreeing to resume negotiations; Nadia meets Lely again and is given the hostage video. DGSE see that the points diagram has been altered to communicate that Cochise wants to defect. Duflot volunteers to go into the field and handle both cases himself. In Iraq, the FSB spy escapes into the desert with Debailly, with IS in pursuit. Meanwhile, Mossad persuades Marina to speak at a seismology conference in Baku. Simon, Marina's ex who works for DGSI, offers his help if she runs into trouble.

Shahanah is murdered by the Iranians. DGSE sets up a secret meeting between Duflot and Cochise near Jarabulus, and Duflot prepares for his mission. Lely asks to meet Nadia again, and DGSE suspects IS may have lost Debailly; their agents in Iraq confirm he has escaped. Meanwhile IS catch and kill the Russian spy, but Debailly manages to evade capture.