The first question that is asked in “Anatomy of a Fall,” a new film from the French director Justine Triet, is a simple one: “What do you want to know?” The line, which could stand as a motto for the whole movie, is spoken by a writer, Sandra Voyter (Sandra Hüller), in a chalet in the Alps. She is being interviewed by a graduate student, Zoé (Camille Rutherford), although their conversation is soon drowned out by a rumpus from above—specifically, an instrumental version of “P.I.M.P.,” by 50 Cent, played with a thunderous boom by Sandra’s husband, Samuel Maleski (Samuel Theis), who is also a writer. Either he’s deliberately sabotaging the interview or he wants to trigger an avalanche.

Of Samuel himself we see no sign, for the moment, and that matters. It foreshadows how the story will unfold. So much in “Anatomy of a Fall” is overheard, heard but not seen, seen but misunderstood, misremembered, conjured out of conjecture, or unwisely taken on trust. When we do catch sight of Samuel, he’s dead—sprawled in the snow beside the chalet, with a deep cranial wound and a trail of blood. So, did he tumble over a balcony or was he shoved? Did he hit his head on the edge of the shed below, or had the blow already been struck? Did he perish by his own hand, or at Sandra’s? Is 50 Cent a suspect? The puzzles proliferate. Warning: Do not expect them all to be solved.

Sandra and Samuel have a son, Daniel, aged eleven, who is played by Milo Machado Graner with a fine blend of frailty and determination. Daniel’s border collie, Snoop, is played—in an equally striking performance—by Messi, whose skill would be the envy of his namesake. Snoop is not just Daniel’s companion but his helpmate, because Daniel was hurt in an accident, when he was four, and left with severe visual impairment. (Typically, the details of that event, and its long aftermath, take a while to emerge. Triet is a specialist in the slow leak.) It’s he who returns from a walk with Snoop, discovers his father’s body, and cries out to Sandra. The music is still blasting forth, but she hears the cry. How come?

We have yet to reach the opening credits, and Triet has got us where she wants us. This is not a sleuthing movie; there are cops, but they mill around the fringes of the plot, and there’s no Poirot to slalom in from a nearby valley, brush the snow from his mustache, and address the case. Instead, we become the detectives—reading every rune, probing for holes, and testing the evidence as if we were treading on ice. “I have to understand,” Daniel says, and his compulsion is infectious. What demands clarification is not only the crime, if crime it was, but the state of his parents’ marriage, which has been cracking and melting for some time. According to Sandra, it was based on “intellectual stimulation.” So much for love.

There is almost no aspect of this tale that doesn’t feel slippery to the touch. Sandra is German but came to live here in France, where Samuel grew up, and is clearly unsettled on what she calls his turf. Speaking largely in English, the language in which—as a compromise, or in search of common ground—they raised Daniel, she is a mother with no use for her mother tongue. She admits to sleeping with other people while she was married, and now, to add to the tangle, she acquires the services of a louche lawyer, Vincent Renzi (Swann Arlaud), with whom she was once involved. He’s badly needed, too, because Sandra is charged with Samuel’s murder. “I did not kill him!” she exclaims to Vincent, urgently answering a question that he hasn’t even asked—maybe the most startling irruption in the film. Regardless of what Vincent privately believes, however, his plan, for the defense, is to claim that Samuel committed suicide. And so to trial.

“Anatomy of a Fall,” which won the Palme d’Or at this year’s Cannes Film Festival, has been widely referred to as a courtroom drama. Yes, much of the second half is set in court, in Grenoble, but you seldom get the impression that Triet—who wrote the screenplay with her partner, Arthur Harari—is enmeshed in the machinery of the law. Indeed, fans of legal shows, on TV, or of Otto Preminger’s crisply organized “Anatomy of a Murder” (1959) will be taken aback by the free-form nature of the proceedings in Triet’s movie. Lawyers, witnesses, and a “spatter analyst” or two seem to interrupt one another at will, or at random, often from a seated position. The prosecutor (Antoine Reinartz), a shaven-headed smirker, roams around snapping and snarling, and I, for one, would toss him out of a high window without a second’s hesitation. What the setting most resembles is a brasserie full of squabbling law students, and you half expect the clerk of the court to arrive with bowls of onion soup.

The most telling sequence focusses on Daniel, as he stands there being quizzed, by both the defense and the prosecution, on his testimony. The camera swivels from side to side, hardening the sense of his being under siege, and the movement prompts two thoughts. One, can a child be cross-questioned, whatever the jurisdiction, in this hostile manner, and, if so, why should the evidence be ruled admissible? Two, has Triet worked on us to such mischievous effect that we no longer care about what is plausible, and crave only the tussle of wills at the movie’s heart? This is less of a courtroom drama, I reckon, and more of a discordant, highly strung character clash with legal bells and whistles tacked on. Notice how we finally get wind of the verdict: not in court, in a formal announcement, but via a television reporter outside who hears an excited hubbub swelling behind her. Truth is not crystalline and clear. It lies in pieces, and you have to pick them up as best you can.

A practical tip: “Anatomy of a Fall” is formidable stuff, and you should arrange to watch it at the cinema with your most captious friends, preferably at six o’clock, so that you can thrash things out over dinner—fondue, I’d suggest, for that handy whiff of bubbling Alpine chaos. Notwithstanding the verdict that is delivered in Grenoble, it’s perfectly possible that you will remain uncertain as to whether Sandra is guilty, and here’s the kicker: even the person playing her doesn’t know for sure. Hüller has revealed that, during the making of the film, she repeatedly asked Triet if Sandra did or did not do the deed. Triet refused to squeal.

The miracle is that such uncertainty renders Hüller’s performance sharper rather than vaguer. It is as though Sandra, reportedly described by her husband—an enfeebled soul, and a less successful writer—as “quite castrating,” had armed herself against all eventualities and foes. With her flustered froideur, she needs no cross-examination to make her bristle, and our response is to marvel at the depths of her discomfort, and perhaps her guile. When she stands outside on a frosty night, drinking and flirting with her lawyer, is she grabbing a rare chance to relax, or subtly swaying him yet further to her cause? How much we like or dislike Sandra is of no consequence. What’s unnerving is that we can’t decide, from one scene to the next, how secure we are in wanting to root for her.

Hüller was in an earlier and less coherent film by Triet, “Sibyl” (2019), which, weirdly, features a guy named Maleski, like Samuel, and a vulnerable boy named Daniel. In both films, moreover, conversations are surreptitiously recorded. In “Sibyl,” a shrink tapes the outpourings of a patient; now, in “Anatomy of a Fall,” we learn that Samuel taped a tempestuous argument that he had with Sandra, not long before his demise. The result is played aloud in court, and, along the way, Triet transforms it into a flashback, meaning that we see as well as hear the marital storm—a privilege denied to the judge and the jurors. (The irony is that the spareness of the audio version makes a greater impact.) Is that a smooth creative sleight of hand, or is the movie cheating on us? Might it be that Triet is following the crafty lead of her own heroine?

The fact that such doubts and reservations encircle this film is not a mark against it. On the contrary, they honor its capacity to provoke. That is why Daniel carries such moral weight. When he confesses, “I got mixed up,” he is being honest—more so than any of the adults—about the nature of confusion. Looking at the veiled gaze of his troubled eyes, which both see and fail to see, we can’t help wondering: when, and under what emotional pressure, does a memory shift from being a reliable account of something to a story that we tell ourselves about what we wish had occurred? It’s no surprise that Daniel should be prey to that slippage; after all, he’s the son of two writers, and he listens as the prosecutor reads out menacing passages from one of Sandra’s books in a bid to incriminate her. (Nice try, Maître. Pursue that line and you’d have prisons crawling with novelists.) Forget the clever tricks, though. If you really want to find out what happened that fateful day at the chalet, there’s only one course of action. Ask Snoop. ♦