Bill Marks (Liam Neeson) is a Federal Air Marshal on a transatlantic flight. He is contacted via text messages on his phone by somebody threatening to kill a passenger every 20 minutes until the hijacker's demands are met. This person knows everything about Bill's personal life including his alcohol problems.
The situation gets rather complicated because the hijacker is playing games with Bill. He can only put his trust in very few of the passengers and crew and he is having a hard time figuring out who is the hijacker among all the passengers and crew.