Dr. Matthew Nolan goes to a medical conference in Beijing, where he narrowly escapes a life-threatening situation at a nightclub before crashing his car on the central reservation. Back in London, he is arrested by the UK Border Force and denied basic necessities while strip-searched, revealing a stab wound from the nightclub incident. Accused of killing a woman named Shen Zhào in Beijing, Nolan is pressured to provide a list of his contacts there. His colleagues who arrive back in London are requested to return to Beijing by the Home Office following China's request, with one colleague abducted by unidentified men when he refuses. MI5 Director-General Madeline Delaney reluctantly agrees to the Chinese trade minister's extradition request due to ongoing negotiations on a Sino-British nuclear power programme. Despite Nolan's denial of the murder allegation, he is extradited to China under the escort of DI Hana Li, though not before he makes a scene in the departure lounge, which causes him to become a viral video. On the North China Air flight, a passenger dies after consuming a vegan meal intended for Nolan, raising suspicions that someone onboard wants Nolan dead.

Despite the passenger's death, Chen refuses to turn around the plane and insists on flying to Beijing. Hana comes to accept Nolan's story after a fellow passenger's dog dies after eating some of Nolan's meal. Following clear air turbulence, co-pilot Wu discovers the circuit boards for the plane's flaps have been disabled but Chen hushes up the incident. One of Nolan's colleagues, Dr Steven Hurst, is subsequently found dead with a broken neck. With Nolan's help, Hana ascertain that Steven was murdered. They also join forces with Air Marshall Zhang to investigate Steven's death. Chen forces a reluctant Wu to report the recent deaths as accidents. To complicate matters, Steven's wife, Dr. Amber Hurst, assaults Dr. Ward for having an affair with her late husband. A grieving Amber convinces Zhang to allow her to spend time with her late husband but is confronted by a stranger. Back in London, Hana's estranged sister Jess sees the viral video of Nolan at the airport being arrested by Hana and launches her own investigation, seeking to publish a news story. She interviews Hana's police superior and learns that Hana is travelling to Beijing. Meanwhile, Delaney's oversight of the Shen Zhào case is complicated by the involvement of MI6 intelligence officer John Tennant.

Hana and Zhang both ask Nolan to recount the events of the conference. In a flashback, Nolan meets Shen Zhao, the woman he is accused of murdering, at the conference bar. While at a night club, she drugs him. Nolan is attacked by bar security, sustaining a stab wound. Following a car accident, he flees to his hotel, where he staples his wound to stop the bleeding. Back in the present, Amber is found dead in the crew area. While examining Amber's body, Nolan discovers that she sustained similar injuries to Steven. Zhang arrests Dr Ward as a suspect in Steven and Amber's murders. Hana updates Madeline, who fails to convince the Chinese trade minister to recall the plane. After Dr Ward disappears, Hana, Zhang and the crew conduct an extensive search of the passenger compartments. When the search is unsuccessful, Hana and Zhang convince a reluctant Chen to let them search the hold. In London, Jess secretly visits the office of General Pacific Medicine, the company that organised the conference Nolan and the other doctors attended. She finds unidentified government workers raiding the building and flees when discovered. Despite Hana's warnings, she visits the London residence of Sir George Chapman, the CEO of General Pacific Medicine.

Aboard the North China Air flight, Hana and Zhang's search of the hold turns up empty-handed. Nolan along with Hana and Zhang discover Dr Ward's corpse stuffed into a crew storage compartment. Examining the remains, Nolan finds that her fingers were broken during the assault. With Captain Chen's help, Han and Zhang search the passengers for the murder weapon, believing the murderer is aboard the flight. Nolan also contacts Sir Chapman, requesting his help once he lands in China. Meanwhile, Chapman questions Jess, who convinces him that she is indeed a trainee journalist. The two are pursued by the sniper Eric Jones, a CIA operative sent to assassinate Chapman. Chapman is killed but Jess escapes and updates Hana about her situation. After discovering CCTV footage of Jess at General Pacific Medicine's headquarters and Chapman's mansion, MI5 Director-General Delaney seeks help from the CIA station chief Mike Maxwell in identifying Jess and learns about her relationship with Hana. Delaney also confronts Tennant, who reveals that General Pacific Medicine was a front organisation for MI6 seeking access to Chinese medical technology. The doctors are unaware that they are unwitting operatives for MI6. Elsewhere, police find the remains of a fifth doctor from the conference, who was kidnapped after declining to return to China.

With Hana's help, Nolan extracts a nano SIM card from his torso wound that was sustained during the bar fight. The SIM card contains files relating to the Anglo-Chinese nuclear deal. Before they can transmit the files to Delaney, a hooded operative sabotages the plane's internet server. Zhang is revealed to be colluding with the hooded operative, who murdered the other three doctors during the flight. During a fight, Nolan kills the hooded operative while Zhang kills himself with cyanide. After discovering that one of the flight crew smuggled a suitcase with fake passports and cash implicating Hana as a Chinese intelligence operative the two deduce that Zhang and his accomplice's plan was to crash the plane and frame Hana. Hana and Nolan force the captain and co-pilot to fly the plane back to London. Meanwhile, Jess is taken into protective custody by MI5. When the British Prime Minister removes Delaney as head of the operative replaces her with Tennant, Delaney escapes with Jess. Their plan is to meet Hana's plane at the airport. Delaney contacts Mike Maxwell for help, unaware that he is Eric Jones' superior.

In a flashback scene, CIA operatives led by Mike Maxwell monitor Nolan and Shen Zhào at the night club as part of an American operation to sabotage the Anglo-Chinese nuclear deal. After failing to stop Zhào from injecting the nano SIM card into Nolan, Maxwell and Eric Jones murder her and plant her body in Nolan's car. Hana and Nolan's plane lands at a British military airbase in London but escape Tennant and MI6 with the help of Delaney and Jess. Meanwhile, British security forces identify Zhang and the other operative as freelancers working for a CIA shell company. At the US Embassy, Nolan recognizes that one of the Embassy staff was a staff member at the Beijing night club. Suspecting that the CIA have drugged their drinks Nolan, Hana, Jess, and Delaney overpower their CIA captors. Maxwell attempts to stop them from leaving the Embassy but Jess hands him a Vodafone chip, which he mistakes for the SIM card. After escaping the Embassy, the four send the file to Tennant, exposing a CIA cyber-operation to cause a meltdown in one of the Anglo-Chinese nuclear power plants in order to damage Sino-British relations. Maxwell tracks Hana, Nolan, and Delaney down to the grounds of the Chinese Embassy. Maxwell shoots Nolan but is arrested by Chinese soldiers and handed over to Minister Tang to face justice for Zhào's murder. While recovering in hospital, Nolan proposes to Hana. To avoid damaging United Kingdom-United States relations by exposing the CIA plot, Delaney allows Hana to break a story about MI6 using doctors as unwitting couriers for intelligence operations. During a family gathering, Hana provides her father with files on her mother supplied by the British government.