DGSE makes contact with Algerians holding Cyclone, and Sisteron goes to Algeria. The Syrians continue to investigate Paul Lefevbre, testing him by mugging him in the street. They also seek help from the Russians. Meanwhile, DGSE puts Marina through a surprise mock interrogation. DGSE is also concerned that Cyclone's capture could have compromised the Sahara Desert operation, in which the Americans are involved. In flashforward, Debailly continues to recount his story to the Americans.

Debailly continues to investigate the leads on Cyclone. Nadim traces Debailly's daughter Prune and starts asking about him. Marina and another agent force a colleague at the Institute to refuse the secondment to Iran. Debailly realises that the Syrians and Russians are tailing him, and finally tells Duflot about Nadia and her involvement with the Syria talks. Meanwhile, the DGSE identifies who is holding Cyclone for ransom in Algeria.

Nadia refuses to betray her country, and is angry at Lefevbre's revelations. Ill from the stress of her situation, she confesses to Nadim, and is flown back to Syria. The Russian FSB confronts DGSE and buys its silence. In Algeria, DGSE fails to plant a bug on the General holding Cyclone; Cyclone is handed over to ISIS. Marina is trained to deal with interrogation by Marie-Jeanne, tested by an Iranian agent pretending to be Reza's wife, and offered the Iran secondment. In flashforward, Debailly continues to talk to the CIA; the Americans do not fully believe his story.

ISIS threatens to execute Cyclone; Debailly is asked to work on his rescue. Nadim tries to blackmail him with Nadia's life, wanting him to betray Syrian sources; Debailly refuses to do so. The Americans pull out of the Sahara operation; DGSE suspects they may have a mole. Marina is further tested before leaving for Iran. Debailly shares details of the rescue plan for Cyclone with his colleagues.

Debailly asks DGSE to help Nadia, but is refused. He attracts the CIA by approaching the Syrians, purporting to represent the Americans, and takes time off to meet the CIA (revealed as the flashforwards shown from Episode Two). Dr Balmes suggests his motivation is not love for Nadia, but craving for the double life he experienced undercover. He agrees to return to the DGSE as a CIA double agent. Meanwhile, Marina disappears in Tbilisi en route to Iran, kidnapped by the Georgian secret service to see from where she seeks help. Cyclone is rescued in an ambush near the border with Mali.

Marina begins to socialise with young Iranians, including Zamani, the son of a well-connected minister. She finds adapting to the internal politics a challenge. The Americans fail to rescue Nadia in an ambush in Lebanon. Debailly threatens to withdraw co-operation; the CIA retaliates by threatening to betray him, then asks him to make a better offer. Debailly offers to share a prospective DGSE source within Iran's nuclear industry. The DGSE discovers that one of the IS executioners, Boumaza, is a French national.

Debailly recalls when he first met Nadia, and continues to agonise about her fate. The CIA confirms its interest in Zamani, but Debailly and Marie-Jeanne fall out over Marina's mission; Debailly persuades Deflot to replace her with him as Marina's handler. Debailly tells Marina to get close to Zamani. The Iranian secret police take an interest in Zamani and Marina. The French Government authorises action against Boumaza; Cyclone cultivates the jihadist's family, and Sisteron poses as a supportive lawyer. Duflot continues to hunt for the mole inside the Bureau. Nadia is held prisoner in Syria.

DGSE receives a report that Nadia has been executed in Syria, but the CIA has warned Debailly to anticipate false reports, and agrees to work with him in return for his Iranian source. Marina is interrogated by the Pasdaran, then released, and she returns to Paris. Duflot tells Marina not to contact Zamani, who is coming to Paris, but Debailly then tells her to contact him again. Sisteron and the sister arrange to meet Boumaza on the Syrian border, where the Turkish military intend his capture. However, the sister is communicating secretly with her brother. Meanwhile, after a mock execution, Nadia is given her 'freedom', but forced to work undercover for the Syrian government representing its rebels abroad.

Duflot discovers that Debailly disregarded his order to Marina not to contact Zamani, dismisses him for misconduct, and reinstates Marie-Jeanne as handler. But Duflot's boss decides Marina should continue cultivating Zamani. Debailly maintains contact with the CIA. Nadia, visiting France, refuses to see him. Meanwhile, Sisteron sets out with Boumaza's sister to meet the jihadist. Turkish special forces extract Sisteron, but they are ambushed by jihadists and Sisteron is captured. Too late, DGSE discovers the sister's communication with Boumaza.

Boumaza takes Sisteron into Syria. DGSE decides not to attack, to protect its local agents. He hears that Turkish forces have his sister, and exchanges Sisteron for her, after cutting off his foot. DGSE ask Debailly back unofficially to lead a team to hunt Boumaza; he plans assassination using a suicide bomber. Duflot notices, from the GPS history of Debailly's phone, the weekend when it was untraceable (when he was with the CIA). He plants a bug in Dr Balmes's office. Nadia, in Paris, is reluctant to continue her role, but Nadim forces her; she contacts the DGSE for help. Celine arranges for Nadia to meet Debailly. Meanwhile, Marina returns to Iran, tasked with recruiting Zamani. Debailly passes her reports onto the CIA.

Continuing her meeting with Debailly, Nadia insists that DGSE help her escape from her forced role as figurehead for the Syrian rebels. Debailly decides to compromise Nadim by forging his application for asylum; he defects, and Nadia is taken away to a safe house. Debailly and Dr Balmes discover the bug in her office. The CIA stands Dr Balmes down from its service. Meanwhile, the French are close to securing Zamani as a source, only to find he has just been recruited by the CIA. Debailly continues to plan to execute the jihadist.

The suicide bomber pulls out of the mission against Boumaza, and Debailly steps into the operation, travelling to Syria but swearing his team to secrecy. He finishes his letter to Prune. DGSE hears that Marina is being interrogated by the Iranian secret police, who are torturing Zamani. The DGSE meets the CIA and insists that they identify the mole; after being threatened, the Americans name Debailly. Prune finds Debailly gone from his flat, reads his letter, and alerts the DGSE.