Bill Marks, an alcoholic and burnt-out U.S. Air Marshal, boards a transatlantic flight from New York to London. Despite his personal struggles, he takes his job seriously. Shortly after takeoff, Marks receives a series of cryptic text messages on a secure network, threatening that a passenger will die every 20 minutes unless $150 million is transferred to a specified account. As the clock ticks down, Marks scrambles to identify the terrorist among the passengers, fostering a climate of mounting tension and paranoia on board.

As Marks investigates, he discovers the account is in his name, making him appear as the hijacker. This revelation turns both passengers and crew members against him, intensifying his dilemma. His struggle to maintain control grows as he enlists the help of a fellow passenger, Jen Summers. As Marks follows the clues and utilizes his skills to thwart the threats, unseen forces work against him, pushing him to act under pressure while racing against time.