An Atrian 800 aircraft mysteriously crashes over the
French Alps, killing all on board. Mathieu Vasseur, an air safety investigator at the
Bureau of Enquiry and Analysis for Civil Aviation Safety, is given the task of analysing the
cockpit voice recorder. He identifies the sound of someone forcing his way into the cockpit shortly before the crash, leading him to suspect a
terrorist attack. He announces his findings at a hastily called press conference. Mathieu's boss, Victor Pollock, goes missing, so Mathieu is given the job of producing the final report into the crash. After detecting inconsistencies in the voice recorder and a voicemail message recorded by a passenger just before the crash, he reconsiders his terrorist theory, but his doubts are dismissed by Philippe Rénier, the head of the agency. Mathieu gets Pollock's home address from an envelope on Pollock's desk. Driving out to the house, he finds it closed-up and unoccupied. Mathieu breaks a window and enters the house and finds little of interest. He grabs the keys to Pollock's vehicle and removes the SD card from the
dashcam. Footage shows that, a few days before the crash, Pollock had a late-night roadside meeting with Xavier Renaud, who runs Pegase Security, a firm which develops on-board communication systems for aircraft. This leads Mathieu to suspect a cover-up. A pilot tells Mathieu that the Atrian 800 had unresolved problems with the rudder's
anti-stall system, but still received an air-worthiness certificate. Mathieu surreptitiously downloads the relevant test flight data from a computer belonging to his wife, Noémie, who works for Atrian. Noémie is suspended after her bosses at Atrian discover the loss of the data. She angrily confronts Mathieu, accusing him of ruining her career. Mathieu persuades Rénier to use the flight data to run simulations on the anti-stall system, but these fail to reveal any problems. As Mathieu becomes increasingly obsessed with the investigation, threatening his mental health, Rénier transfers him to other duties. An investigative journalist from
Mediapart, Caroline Delmas, tells Mathieu about a man named David Keller, a former Pegase employee who was arrested for attempting to
hack an aircraft's communication systems. Mathieu learns that Keller was on board the doomed Atrian 800. As Mathieu prepares to hand over his files to a colleague prior to his transfer, he realizes one of them has been modified by Pollock. The new version contains GPS coordinates, which he traces to a pond behind Pollock's house. There he discovers the original voice recorder from the crashed plane. He uses equipment in Pollock's house to analyse the recording, and thus discovers the truth about the crash (which is shown in a flashback). On board the doomed plane, Keller used a laptop to take control of the aircraft's systems, not because he wanted it to crash but to demonstrate faults in the Pegase systems. But the hack goes wrong, and neither he nor the pilots are able to regain control, thus causing the aircraft to come down. At the end of the recording, Pollock appears in a video. He confesses to tampering with the voice recorder, having been
blackmailed by Renaud into covering up faults in the Pegase systems. As he watches the video, Mathieu becomes aware of two men entering the house, apparently looking for him. He flees, but not before sending the recording and the video to Noémie. As he drives away at speed, he loses control of his car in a manner that suggests that the car's control systems have been hacked in a way similar to those of the crashed plane. The vehicle crashes into a tree and Mathieu is killed instantly. When Renaud gives a presentation at the
Paris Air Show, Noémie patches the video of Pollock's confession into the show's audio-visual system, where it is seen by an audience of industry leaders and journalists. At the same time, the news breaks out in the media. As Noémie walks away from the presentation, police arrest Renaud. == Cast ==