François Cluzet plays “Beck,” a pediatrician who is preparing for a late-night swim with his wife “Margot” (Marie-Josée Croze) when he hears her scream and then is struck on the head, falling into the water. The story jumps forward eight years to reveal that Margot was murdered and someone else has been found guilty of the crime. Each year, Beck visits his former in-laws for the anniversary of her death, but this time he’s unusually unsettled because a strange email has made him question everything about what happened. Things begin to feel inconsistent, not just for him, but seemingly for others as well. The discovery of additional bodies near the lake prompts the police to reexamine the original conviction and consider Beck himself, along with the possibility of a €200,000 insurance payout. As the investigation intensifies, he turns to the father of one of his patients—a man acquainted with both sides of the law—and enlists the help of Margot’s former best friend “Hélène” (Kristen Scott-Thomas) to uncover the truth amidst a confusing array of information. The film provides hints and misleading clues as the suspense builds, leaving viewers questioning everyone's motives and even whether "Margot" is truly deceased. Beck faces dangerous situations involving criminals and a particularly ruthless character who seems ripped from a “Bond” movie. However, I felt the ending faltered somewhat. While the first two hours were engaging and puzzling, the final resolution reminded me of an Agatha Christie novel where previously unimportant details about various characters—some minor, some more significant—reveal connections that are ultimately effective but feel rushed and incomplete. Cluzet gives a lively performance, the dialogue effectively communicates everyone's anxieties, and the central mystery remains compelling overall.

Source on TMDB