Two U.S. Air Marshals, Jack Hammond and alcoholic Bill Marks, board a flight from New York City to London. Marks sits next to Jen Summers, who has switched seats so she can sit by the window. After takeoff, Marks receives a text message on his secure phone stating that someone will die every 20 minutes unless $150 million is transferred to a specified bank account. Marks breaks protocol and consults Hammond, who dismisses the threat. Marks has Summers and flight attendant Nancy monitor the security cameras while texting the mysterious person to try to identify him.
When Hammond is seen using his phone and suddenly goes to the rear toilet, Marks confronts him. Hammond tries to bribe Marks, and attacks. Marks secures Hammond in a chokehold, and as Hammond raises a gun, Marks kills him exactly at the 20-minute mark. Marks finds cocaine in his briefcase, and learns the perpetrator had blackmailed him and set him up for death. He alerts the TSA, but TSA agent Marenick informs him that the bank account is registered in his name and accuses Marks of being the perpetrator. Pilot David McMillan dies, apparently poisoned. Kyle Rice, the co-pilot, convinces Marks that he is innocent.
Marks searches the resentful passengers. One of them uploads a video in which Marks accuses and manhandles schoolteacher Tom Bowen, convincing the rest of the world that Marks is the perpetrator. Kyle is instructed by the TSA to divert to Iceland. Marks persuades programmer Zack White to write a computer virus to make the hijacker's phone ring. The phone rings in passenger Charles Wheeler's suit pocket, but he denies it is his. As Marks roughly questions him, Wheeler suddenly dies, foaming at the mouth.
In the first-class lavatory, Marks discovers a hole drilled into the wall that offers a clear shot to the pilot's seat, and discovers a dart in Wheeler's body. A passenger tells him Summers entered the lavatory recently. Marks accuses Summers of being the hijacker. Summers becomes upset, as she had stood by him, and convinces him of her innocence.
Two RAF Typhoon fighter jets meet the plane to escort it to a military base in Iceland. Summers and Marks unlock the hijacker's phone, unintentionally starting a 30-minute timer for a bomb. Through words in a television news report claiming that Marks is hijacking their flight, Marks realizes that the bomb bypassed the security checks, and finds it in Hammond's cocaine briefcase. When some passengers attack Marks, Bowen stops them, believing that the bomb is the priority. Marks convinces the others of his innocence, and has them move the bomb to the rear and surround it with luggage to direct the blast outward, while everybody moves to the front of the airplane. Marks tells Kyle to descend to 8,000 feet, as the current pressure differential will destroy the airplane if the bomb explodes, although the escorting jets refuse to let Kyle deviate from his course.
Marks, watching the earlier video, notices Bowen planting the phone on Wheeler, implicating Bowen as the mastermind of the murders; White is Bowen's accomplice. Bowen reveals that his father was killed in the September 11 attacks and blames the U.S. for not improving their security enough to prevent future similar attacks. Their goal was to frame Marks as a terrorist, thus ruining the reputation of the Air Marshals Service to force the U.S. to create stronger security laws. Marks persuades White, who was in it for the money, to try to disarm the bomb. Bowen, who wishes to die on the plane in a suicide mission, double-crosses White. Kyle descends the plane to 8,000 feet, giving Marks the opportunity to kill Bowen. White attacks Marks, still wanting to escape the aircraft, but the bomb detonates, killing him and blowing open the back of the plane.
Despite the damage, Kyle lands the plane in Iceland. Marks is praised as a hero. He and Summers make plans for a possible night on the town.
Liam Neeson as Bill Marks,
Julianne Moore as Jen Summers
Scoot McNairy as Tom Bowen
Michelle Dockery as Nancy,
Nate Parker as Zack White
Corey Stoll as Austin Reilly,
Lupita Nyong'o as Gwen,
Omar Metwally as Dr. Fahim Nasir,
Jason Butler Harner as Kyle Rice,
Linus Roache as David McMillan,
Shea Whigham as Agent Marenick,
Anson Mount as Jack Hammond,
Quinn McColgan as Becca,
Corey Hawkins as Travis Mitchell,
Frank Deal as Charles Wheeler,
Bar Paly as Iris Marianne,