Bill Marks, portrayed by Liam Neeson, is a troubled U.S. federal air marshal battling alcoholism, having entered the Air Marshal service after departure from the police force. While on a non-stop journey aboard British Aqualantic Flight 10 from New York to London, chaos ensues when he receives alarming text messages on his secure phone. The messages inform him that a passenger on the plane will perish every 20 minutes unless a hefty sum of $150 million is transferred to a specified bank account.
Breaking standard protocol, Marks confides in fellow air marshal Anson Mount, only to discover that Hammond is involved in a cocaine smuggling operation. During a struggle, Marks tragically kills Hammond in a lavatory, marking the onset of terror with the first death occurring exactly at the 20-minute interval. To buy time and unravel the identity of the Texter, he collaborates with his fellow flight crew and Julianne Moore, who is seated next to him.
The situation escalates when the aircraft's captain suddenly dies due to poisoning, leading passengers to suspect Marks of hijacking the plane. With the bank account linked to him and incriminating footage of him acting aggressively going viral, public perception shifts dramatically against him. Co-pilot Kyle Rice, behind the controls, hesitates to disregard Marks despite TSA directives to land the plane in nearby Iceland. Marks enlists the help of Nate Parker, a cell phone programmer, to create a diversion that would ring the Texter’s phone. They locate the phone in the pocket of another passenger, who vehemently denies any connection.
In a shocking turn of events, Marks discovers a hidden mechanism—holes in the lavatory wall—allowing for the discreet shooting of poison darts at the captain and other victims. As he and Summers attempt to gain control over the Texter's phone, it catastrophically activates, sending out false alerts proclaiming Marks as suicidal and implying there is a bomb aboard. While searching around, Marks stumbles upon the bomb stashed within the cocaine that Hammond had attempted to smuggle.
Faced with time running out and unable to land immediately, he resorts to a drastic protocol intended to minimize damage, first bringing the aircraft to 8,000 feet to stabilize pressure. His plan involves covering the bomb with luggage at the back of the plane and relocating passengers to the front. However, this leads to a violent altercation when passengers, influenced by media narratives, believe he’s the real threat. In a grand moment of teamwork, passenger Scoot McNairy comes to Marks' aid, using his weapon to control the emotional crowd.
After piecing together the puzzle, Marks realizes that Bowen is behind the nefarious acts, with a tortured past linked to the 9/11 attacks fueling his motive. Unbeknownst to the others, Bowen seeks to expose glaring vulnerabilities in airport security by framing Marks. Daring confrontations ensue, resulting in Bowen shooting White amid chaos. In a climax filled with tension, Marks ultimately takes down Bowen, but not before White, in his fervor, attacks him—meeting a tragic end in the ensuing explosion.
The plane barely manages an emergency landing in Iceland, thanks to Rice, who bends the rules amid a standoff with fighter jet escorts, managing to save all onboard. Despite the harrowing ordeal, Marks garners public recognition as a hero, with the story concluding on a hopeful note as he begins to build a new friendship with Summers.
