Agent Malotru (Debailly) is recalled to Paris after six years undercover in Damascus, and ends his affair with Nadia El Mansour. In Algiers, agent Cyclone is arrested, drunk, despite being avowedly teetotal. Debailly struggles to forget Nadia and to return to a more normal working life. He is assigned to train Marina Loiseau, who will work undercover in Iran. Debailly discovers that Nadia is in Paris and resumes contact with her. Meanwhile, agent Cyclone has gone missing in Algeria.

Marie-Jeanne presents her candidacy to succeed Michel Ponte as director of the service. An Uzbek tourist in Paris finds a weapon. Is he part of Mikhail's revenge?

Debailly is still under routine surveillance, whilst resuming his affair with Nadia under his cover identity Paul Lefevbre. He starts to question Nadia's reason for being in Paris. Meanwhile, the DGSE hires psychologist Dr Balmes, and asks her to review his state of mind. Agent Gherbi is exfiltrated from Algiers after hearing about Cyclone, and Marina continues preparing for her mission. The episode closes with a brief scene of Debailly recounting his story while connected to a polygraph.

A meeting between the different chiefs of the Sinai tribes is to be held at the Nile Sorman hotel where Marie-Jeanne is working undercover. Fouad, the Egyptian security officer, travels to Paris for a meeting with the Bureau. Marina joins Andrea in Jordan to help him in his mission.

Marie-Jeanne is back at the Bureau. Sisteron processes information from Karlov. Mikhail must explain to his wife and son the difficult situation they are in. Jonas discovers that the young woman with whom he has had an affair for several weeks is working ... for the Russians.

Marina starts work at the Institute of Earth Physics. A brief scene shows Debailly, connected to a polygraph, continuing to recount his story. The DGSE interrogates Gherbi to confirm he is not also working for Algerian intelligence. Duflot's brother-in-law works undercover in the Sahara Desert. Meanwhile, Nadia's visits to Lefevbre arouse the suspicion of Syrian agent Nadim. Debailly digs into Nadia's background, and confronts her as to why she is really in Paris.

JJA, the director of Dsec, has taken over the leadership of Le Bureau, while Marie-Jeanne has moved to Egypt. A newspaper article on the events in Ukraine emerge. The agency fears they have a leak.

On his way to Riga, Sylvain disappears at Moscow airport. Marie-Jeanne is in the Sinai desert. She must work alongside the Egyptian agent Ramsès.

Liz Bernstein and La Mule are quietly continuing their investigations to identify the mole in the service. After a few weeks of rest in Sologne, Marina finds her post in Paris. Sisteron is responsible for training Andrea on the computer programs used by Israeli hackers. Meanwhile, in Phnom Penh, Sylvain decided to collaborate with the group led by Véra. In Paris, his superiors questioned his ability to manage the danger associated with this mission.

The episode starts with a flashforward of Debailly continuing to explain his story. Nadim investigates Paul Lefevbre, and tells Nadia not to see him again. But he finds them having dinner, and interrogates Lefevbre. Nadia confesses her true reason for being in Paris, and Debailly realises that their relationship puts her in danger. Meanwhile, Reza starts to flirt with Marina, and she has to rebuff his advances. DGSE tries to find out if the Algerians are holding Cyclone, and must stop his mother travelling there to search for him.

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.

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.

Malotru is in place in the Russian agency FSB as "Pavel Lebedev". Sisteron is sent in the greatest secrecy to Cairo. Meanwhile, Jules announces to JJA that he has located Sylvain's phone. Digital tracing indicates that Sylvain is in Phnom Penh, Cambodia.

Debailly continues to be tailed by the Russians. The DGSE meet an Algerian with information about Cyclone. They decide to recruit Nadia; Marie-Jeanne realises that Debailly has not told her the full truth, and confronts him. She also helps Marina compel a second colleague to refuse the Iran secondment, and teaches Marina a lesson about not getting close to her contacts. Debailly continues to be interrogated by the CIA in flashforward; it is revealed that Dr Balmes works for the Americans.

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.

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.

In Moscow, Malotru welcomes César, who has taken Ellenstein’s identity. Back in Damascus, the Syrian authorities refuse to let either Jonas or Jean-Paul access the morgue, where Iode 3’s body most likely lies.

At the DGSE, the work of JJA is carefully examined. Dsec is particularly interested in the way he manages Pacemaker, who is on a mission in Cambodia. In Cairo, Marie-Jeanne discovers that her hotel room has been bugged. Pacemaker is closely watched at work.

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.

The DGSE recruits the jihadist's sister, planning to trap and kill Boumaza. Meanwhile the Iranian secret police continues to investigate Marina, and DGSE discovers this from a source. Marina is recalled to Paris, but leaves on an expedition before receiving the message, and is arrested. In Syria, Judge Badran interrogates Nadia about her affair. Duflot suspects that Dr Balmes, who has resigned from the DGSE, may have been the CIA mole, but fails to find any evidence.

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.