Corporate business negotiator Sam Nelson boards Kingdom Airlines flight KA29 from Dubai to London to return to his estranged wife. At the airport, he convinces gate staff to allow fellow passenger Alec on after he narrowly misses the gate closing. After takeoff, teenage passenger Naomi finds a bullet in the bathroom and tells Marcus, a friendly fellow passenger. Marcus, secretly part of a hijacking crew, informs leader Stuart and his colleagues to expedite the takeover. Using Glock 19 pistols hidden in toiletry bags, several hijackers take control of the plane, speaking both English and Arabic. Airport screener Neela, who allowed the guns on board, returns home when her husband and child are threatened. The hijackers access the cockpit by threatening Collette, a flight attendant who Captain Robin Allen is having an affair with. Before the Wi-Fi is turned off, Sam is able to text his wife about the incident, and she passes it to her boyfriend, DI Daniel O'Farrell, who works for the Metropolitan Police.

Two passengers attack one of the hijackers, and Sam picks up his gun. The passengers are subdued, and Sam returns the pistol to Stuart Atterton, the lead hijacker. O'Farrell contacts his ex, DCI Zahra Gahfoor from SO15, who reaches out to colleagues at Heathrow Airport, who state the KA29 call was a false alarm. He relays this to Marsha. Abdullah, the Dubai flight controller whom Allen assured everything was fine, has doubts about KA29's status. He notices Neela leaving security screening on CCTV, before her shift ends. Allen is removed from the cockpit, and tells Sam that the Iraqi military will be contacted when they enter their airspace and nobody responds. However, the hijackers force Allen to confirm to Baghdad ATC there is no issue. At Heathrow, air traffic controller Alice Sinclair also questions the "false alarm" and notices a slight deviation in the flight plan, a post-9/11 indication for help. Arriving at Neela's house, Abdullah finds her and her family murdered and is killed by British assassins.

Sinclair calls Gahfoor about her concerns, who then escalates the matter to the Home Office and JTAC. Passenger Yussef, a former Egyptian Army officer, thinks the hijackers are using blanks, but can't be sure. Arthur, a flight attendant, tells Sam about the bullet Naomi found. Sam works with the flight crew to get a drawing of a real bullet and blank round to Naomi, who identifies the latter. Atterton calls their superior to update them, but the call goes to voicemail. Tindall, a senior official, calls in Foreign Secretary Louise Aitchison. Gahfoor sends the KA29 manifest to O'Farrell, who notices that five names (the hijackers) do not appear on any national databases, but their passports seem legitimate. Hijacker Jaden attacks Nasir, a passenger trying to get insulin for his uncle. In the melee, a child, Lizzie Miller, goes missing, and Sam sneaks to the back of the plane to attack Marcus and disarm him but is overpowered. Atterton swaps his blanks for live rounds and approaches the back. Challenged by Sam, Marcus raises his gun. A shot is fired.

Atterton executes a passenger as a warning. In the melee, Lewis is stabbed by a passenger. Atterton tells Lewis they are doing the hijack "for Edgar and John". Sam is tied up by Marcus but soon released to provide first aid as Lewis bleeds out. As KA29 enters Romanian airspace without responding, two NATO Eurofighter Typhoons are scrambled with orders to shoot it down as it approaches Bucharest. Aitchison takes control, and the prime minister is called. Whilst helping Lewis call his mother, Sam uses the cellphone to send contact info to Marsha, who passes it to O'Farrell. Checking the PNC, he and Gahfoor ascertain the hijackers' identities, realising they are part of organised crime, not terrorists. Aitchison passes this information to the Romanians, who call off the jets just in time. David, doctor on board, carries out a makeshift thoracostomy on Lewis to stop him from dying. Two more British assassins scope out the Nelson residence. The home secretary is given a list of demands by Devlin, an associate of the hijackers.

As the plane enters Hungarian airspace, Lewis's condition starts to deteriorate. Dubai police are called to Neela's house, and her dog leads them to the bodies of Neela and Abdullah. Meanwhile, the hijackers begin to argue over what to do next. It is revealed that their demands are to get Edgar and John released from prison. The home secretary conveys this to Gahfoor and Aitchison, while the prime minister is on hold. Atterton decides to use First Officer Anna Kovács to get her to communicate to Hungarian ATC that they are landing at Győr Airport and need medical assistance. The Hungarian Counter-Terrorist Unit is immediately dispatched to the airport to neutralise the hijackers. O'Farrell and his associate go to visit Elaine, Lewis and Atterton's mother. Elaine tells O'Farrell about the organised crime syndicate then runs onto a highway, where she is killed by a truck. Terry then tells Sam that their organised crime heads will kill them and their family if they land, as he reveals that they have Sam's family info. Lewis withdraws the pen that David inserted into his chest, effectively killing himself. Atterton sees this and tells Deevia Khan to instruct Anna to stop the landing. Assassins working for the organised crime group enter Sam's home, and Sam's son Kai notices their guns and hides.

Sam's son Kai escapes the assassins by hiding inside a wardrobe. The British government concedes to the demands of the hijackers and releases Edgar and John from prison. However, when the police keep following them, Edgar texts the hijackers to kill one passenger and send a photo. Sam intervenes and convinces Stuart that there is already a dead passenger on board and therefore no need to kill another one. The government task force tracks Edgar's car using drone surveillance and sees that he and John are headed to a nearby airfield. Meanwhile, inside the aeroplane, passengers are beginning to plan a revolt. At the same time, news breaks out in the British media that KA29 has been hijacked and Kingdom Air's stock price falls, as Edgar had hoped. Some of the passengers on KA29 begin fighting the hijackers, when an unknown assailant executes Captain Allen, enters the cockpit and locks it, to the surprise of everyone on board.

The passengers take over the cabin, and Sam convinces Atterton to give up his pistol. The unknown assailant, revealed to be Amanda Taunton, a former Royal Navy aviation consultant, puts the aircraft on course for central London. Sam tries to convince her to allow him access to the cockpit, but to no avail. On the ground, DI Daniel realises that Kai is in danger at Sam's house and rushes there to save him. As the aircraft enters British airspace, the Royal Air Force dispatches two Typhoons to intercept it. On board, the crew have returned the passengers' phones, and London ATC manages to establish contact with Sam. Alice convinces him to tell her the truth about the situation on board. Aitchison pleads with the prime minister not to shoot the plane down and offers to take the blame. Edgar and John bicker over when to close the short on Kingdom's stock, with John shooting Edgar and leaving him for dead. In the meantime, Daniel mounts a successful rescue operation of Kai. On the plane, having found Amanda's phone and learned of her family, Sam eventually convinces her to let him into the cockpit. Fearing for hers and her daughter's life, Amanda is reassured by Walsh over the phone that she will not be arrested, and she reveals to Sam that their plane, flying too low over central London, has no more fuel and will soon flame out. Alice redirects her to RAF Northolt, seven miles away, but before they can reach the airfield, the engines die. Despite this, Amanda manages to land the aircraft, with all passengers safe. Emergency services reach the scene and assist with evacuation while rounding up the hijackers. Atterton, having broken free, shuts himself on the plane in an attempt to shoot Sam, who is still on board. The police storm the aircraft, and after being distracted by Sam, Atterton is arrested.