In early 2020, CIA agent Henry Pelham is summoned by his superior, Vick Wallinger, with crucial news: the CIA has reopened the investigation into Turkish Alliance 127, a tragic 2012 terrorist hijacking. The agency suspects a breach from their Vienna station, where both Henry and Vick are stationed. The break comes when one of the hijackers, Ilyas Shushani, is arrested in Afghanistan and provides significant leads.
Tasked with interviewing Celia Harrison ([Thandiwe Newton]), a former colleague at the Vienna station, Henry is confronted with both professional duty and personal history, as they were once lovers before parting ways after the catastrophic event. He first meets another co-worker, Bill Compton, in London to inform him of his mission to uncover the leak related to Flight 127. Unbeknownst to Henry, Bill promptly alerts Celia about his investigation that same night.
Now living a quieter life in Carmel-by-the-Sea, California, Celia meets Henry at a nearly deserted upscale restaurant where their conversation soon turns serious. Celia discloses that an Austrian intelligence operative, Karl Stein, approached her shortly after she relocated, asking her to inform on her colleagues, particularly Bill, whom Karl suspects of divulging state secrets to extremists. Caught in the balance between their shared past and the present investigation, Henry urges Celia to recount the harrowing events surrounding the hijacking.
Flashing back to 2012, the film reveals a tense scene where Flight 127 is overtaken by four militants of an Islamic terrorist faction while on the runway. The Vienna station, including Vick, Bill, and other agents, springs into action to manage the crisis while attempting to pinpoint Ilyas as a key player, despite him not being on the flight. The hijackers threaten to kill passengers if their imprisoned comrades are not released, giving authorities a strict 24-hour deadline.
Celia, utilizing her contacts, attempts to connect with a source in Vienna, realizing that her dealings may have been compromised when her leaker requires payment for any information. This complexity is further complicated by Henry's past actions where he was forced to betray Ilyas to maintain mutual relations with the Russian government, resulting in catastrophic personal consequences for both.
Amidst this escalating tension, Celia's instincts lead her to question the legitimacy of their communications, suspecting that messages about the hijacking may have been manipulated. Tragically, when demands go unmet, the terrorists resort to releasing Sarin gas aboard the flight, resulting in devastating loss of life and marking a turning point in both Celia and Henry's lives as she heartbreakingly chooses to sever their relationship the following day.
In the present, the atmosphere becomes increasingly fraught as Celia reveals the painful truth to Henry about their breakup: she had spotted a call from a number linked to Iran on his phone. As he grapples with the revelation of being the leak, it becomes clear that her meeting with him was orchestrated by Karl as a setup for a more sinister purpose.
As poison courses through Henry's veins, he attempts to explain his past betrayal: he had been manipulated into revealing crucial information under the guise of protecting Celia. With the weight of truth crashing down, Celia confesses that the dangerous game they played leads back to the very source of their pain, and as Henry comes to term with his fate, Celia must face the life she chose over the broken man before her, returning to her family as Karl informs Vick of Henry’s demise, revealing a deeper conspiracy at play.
