Anyone stumbling into “The Apparition” expecting a Hollywood horror movie will emerge as bewildered as readers seeking titillation were when they put down “Lolita” back in the fifties, and one can only imagine what a hack like Dan Brown would have contrived from its premise. Xavier Giannoli constructs his film like a mystery, too, but one concerned with major issues of faith rather than potboiler conspiracies; and if in the end the resolution is not fully satisfying, one has to be impressed by the attempt.

The protagonist of the film is Jacques (Vincent Lindon), a war correspondent who has just seen his best friend killed in the Middle East. He returns traumatized, with debilitating pain in his ears. While on leave from work, he receives a call from the Vatican asking him to fly to Rome and consider undertaking a special mission: heading a commission to investigate the genuineness of a supposed apparition by the Virgin Mary in a small French town.

After a fascinating sequence in the Vatican archives, during which the agnostic reporter is schooled on the need to look into such supposedly miraculous occurrences, Jacques accepts the assignment and travels to the mountains of southern France, where eighteen-year old Anna (Galatea Bellugi) is the focus of attention among throngs of pilgrims who believe she has witnessed a true apparition. She is a novice in a convent, protected by Father Borrodine (Patrick d’Assumcao), the local priest whom she first approached about her vision. He and Anna’s fellow nuns have taken charge of the occasions on which Anna appears before the believers to offer messages of peace and love; also on hand is a more aggressive clerical promoter, Anton (Anatole Taubman), who is interested in utilizing the internet to spread word of the occurrence and create a market for merchandise associated with it.

The members of Jacques’ team include priests, a psychiatrist and a theologian; some dismiss the girl’s story, others are more open-minded. From his perspective, Jacques is fascinated by Anna herself, and takes it upon himself to investigate, in his reportorial fashion, her past in schools and foster homes. He also interviews witnesses to her conduct at the time that she claims to have had her initial vision. In the process he uncovers discrepancies that raise in his mind serious questions about whether she is telling the truth.

Anna, too, is acting strangely. She takes secret trips to a nearby mall, where she meets a boy keeping a cache of letters in storage for her, and as the investigation proceeds she shows signs of stressing out. The letters, as well as Jacques’ search into her past, suggest a close bond she had with a girl named Mériam, but since she is no longer in the area, the journalist must try to get information about her from others.

“The Apparition” moves with almost glacial slowness—it runs well over two hours—and eschews melodramatic excess, opting instead for a gently probing approach that keeps the viewer as much in the dark as Jacques. It takes patience and attentiveness to follow his accumulation of facts that ultimately will lead him back to the Middle Eastern desert where the film began, in order to confirm the suspicion he’s formed about what actually happened at the time of reputed apparition.

Whether you will find it time well spent, or be satisfied with the revelation Giannoli provides to resolve the central mystery, will depend on your willingness to join Jacques in considering the possibility that the sacred does sometimes intervene in human affairs, and doggedly inquiring into whether this is one of those times. To be honest, Giannoli is more successful in raising the questions than in providing entirely satisfying answers to them, but at least the solution he posits isn’t cheap or tacky, though it might be too clever for its own good.

It is certain in any event that Lindon gives a powerful performance as Jacques, conveying the intensity with which he approaches the Vatican investigation as well as the simmering grief he feels over the loss of his friend: he paints a compelling portrait of a man desperately searching for answers to the most profound mysteries even as he looks into a personal abyss. Bellugi, meanwhile, has the sweet, angelic appearance her role requires, while suggesting the darker currents that lie within. As the two priests d’Assumcao and especially Taubman are inclined to overdo their characters’ shiftiness, but that’s undoubtedly designed to lead the audience to suspect that their motives aren’t exactly pure—and there is a suggestion that the Vatican believes that might be the case as well.

Technically the film is expertly mounted, though some might feel that the pacing favored by Giannoli and editor Cyril Nakache is rather labored. Cinematographer Eric Gautier makes good use of the mountainous locale, and captures some lovely imagery in the interior convent scenes, where the nuns work making quilts and feathers fly in the air, often landing on their habits and leaving them to dust one another off. Production designer Riton Dupire-Clement should be recognized for arranging those images as well.

“The Apparition” is rarefied fare, but it is notable for treating religious themes in a serious, non-dismissive way, and though the ending may strike some as an example of sleight-of-hand that doesn’t quite work, even that can’t undermine its ambitions.