Mikhaïl Karlov receives a parcel with the USB key which Sylvain uses at work. Both surprised and worried, he tries to reach the young hacker and learns that the young man is on a mission in Seoul. Meanwhile, Alexis Bakatine, the head of security at the FSB, is continuing his investigation into the spy "Black September" in order to find out if Pavel is a double agent.

Duflot lectures his team about loyalty, then offers to resign, but his boss refuses to accept. The DGSE investigates Debailly's disloyalty and interviews his colleagues. Debailly takes the suicide bomber's place as cameraman for the interview with Boumaza. In Iran, the CIA has agreed to trade one of its prisoners for Marina, but the Pasdaran try to kill her after encouraging her escape. However, she evades capture and is exfiltrated to France. In Raqqa, Debailly meets and kills the jihadist, but is himself captured and made hostage. Nadia opens the letter he left her, which expresses the same feelings about their love affair that she did, in the first episode of season one.

In Ukraine, Malotru arrives at the exchange location to get Marina. But on the way back, their convoy deviates from the route initially agreed upon by the DGSE, forcing him to warn Sisteron. Back in Paris, Marie-Jeanne quickly understands that Malotru’s life is at stake and confronts JJA and Ponte. Meanwhile, Jonas interrogates Iode 3 to try and prevent an impending terrorist attack in France.

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.

DGSE tracks Debailly's attempts to contact Nadia. Dr Balmes meets her, and explains how Debailly got her released from captivity. Debailly sets up a plan to meet Nadia in a hotel, contacting her via her assistant's mobile, which DGSE is already monitoring for another operation. Meanwhile, Simon tells DGSE about Marina's call for help; he suspects she is being held in the hotel, and plants a microphone in her room. The agent is told that a Mossad team is coming to deal with her, which DGSE overhears. Marina is saved at the last minute when DGSE blow her cover. In Syria, the French pull out of helping the Kurds, but leave Esrin in place; she is killed in the fighting. In France, DGSE arrive at the hotel to apprehend Debailly, but Nadia warns him using their agreed code. Nadia is taken away, and Debailly disappears into the night.

Sisteron warns Marina that her cover has been blown, but that her arrest could help on another crucial assignment. Meanwhile, Malotru parts ways with Samara and comes back to France, where he is to be held in solitary confinement. Back in Syria, Jonas has lost Iode 3’s track and must turn to artificial intelligence to try and find him.

JJA is told to go ahead and recruit Mikhail. He contacts Pavel in Moscow to develop a strategy. Sylvain is sent to Seoul by the Russians to enlist Yellow Joon, a genius hacker. In Paris, Sisteron admits having lost confidence in JJA. In Cairo, intelligence indicates an attack is imminent.

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.

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.

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.

Arrested for Espionage by the Russian secret services, Malotru is tossed aside and left to the mercy of other inmates. Back in France, the DGSE is striving to understand his motives before making a move. Marina’s phone has been hacked and used in a cyberattack against the Boulgakov Centre. Back in Iraq, Jonas suspects that a seemingly repentant Jihadist may be playing him to sneak his way back to France.

Karlov asks Malotru to join the FSB in Moscow. In Paris, Sisteron and the entire Bureau must answer to an inquiry questionnaire on Marie-Jeanne, which JJA intends to use against her during the next board meeting. Meanwhile, Marina is resenting the way the Bureau is using Micha, afraid to once again leave a trail of destruction in her wake.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.