In press notes for the new film “When Fall Is Coming,” acclaimed French writer/director François Ozon asks a ridiculous yet reasonable question: “When we cook wild mushrooms, are we not, more or less subconsciously, trying to get rid of someone?” A bit of the same mix of the farcical and the perceptive describes the film itself, focused as it is on an elderly grandmother who may or may not be involved in her daughter’s death. 

A medley of moral quandaries, the picture works as a simmering psychological thriller before steadily cooling into an intimate drama seasoned with piquant performances. Some viewers, though, may find its open-ended interpretations indigestible.  

A French film and stage actress, Hélène Vincent, plays Michelle, a doddering but still active senior who is a resident of a small town in Burgundy and whose daughter and grandson are Parisians. In its opening scenes, we see her tidy up her house in anticipation of their visit, and collect wild champignons with her best friend, Marie-Claude (Josiane Balasko), who lives alone while her son is incarcerated. Both seem like lovable pensioners as they forage in a forest among fallen leaves and auburn ferns.

Michelle’s sketchy knowledge of edible mushrooms comes to the fore as she prepares a dish for her visiting family members and considers a particular fungal specimen. She consults a guidebook, which indicates the mushroom as poisonous, and places it to the side, but then seems to experience a lapse, similar to an earlier moment in which the character looked a bit lost during an activity. 

Is she having a so-called senior moment or pausing in the midst of some crafty cogitation? This question provides the film with its thematic throughline, as soon her daughter Valérie (Ludivine Sagnier) nearly dies from consuming the mushrooms — Michelle and grandson Lucas abstain — and later on does die while back at Paris, after falling from her apartment.

Valérie’s fall is just as morally fraught as the poisoning because it occurs during a visit from Vincent, Marie-Claude’s son recently released from prison. In the lead-up to the tragedy, Vincent helps the well-to-do Michelle around the house and witnesses her distress over not being able to see Lucas since the mushroom incident. 

He subsequently pays Valérie a visit to appeal on her behalf, and their charged yet civil conversation hints at their mothers’ dark pasts. Just before the moment of her fall, though, Mr. Ozon cuts away, as he did after Michelle’s pause during food prep, leaving viewers to wonder what happened next. Did Vincent commit murder in some implicit pact with his mother’s best friend, or did the depressed Parisienne, who was going through a divorce and would smoke on her balcony, simply slip?

Autumnal and ambiguous, the film often feels like a collaboration between directors Ingmar Bergman and Claude Chabrol, with the former’s trademark close-knit tensions melding with the latter’s irrational criminality and droll unease. Mr. Ozon certainly has fun with his story, particularly when he informs us of Michelle and Marie-Claude’s former professions, yet he balances this almost camp element with scenes of doubt, earnestness, and a dour apparition — though even this last ingredient contains some humor.

After Lucas moves in with her, Michelle begins seeing and speaking with her daughter’s ghost, leading the elderly woman to question her happiness and “unconscious” motives. Their relationship was a testy one, with the daughter long blaming her mother for her problems, and Michelle developing a guilty conscience after her death. The bitter interactions between a mother and daughter are contrasted with the idealistic bond between a grandmother and grandson.   

Ms. Vincent committed to a tricky role as Michelle, one that must touch on senility brought on by age, solitude, and despair while predominantly portraying a lucid, benevolent, and reliable person. The movie also requires her at times to suggest a passive intent — a difficult, almost meta aspect — lending her actions an air of premeditation. Subtly and intelligently, the actress succeeds in conveying the part’s complex psychology. 

As Michelle’s friend, Ms. Balasko portrays Marie-Claude’s more cautious, controlled, and slightly jaded persona skillfully, particularly during a scene in which she watches Michelle dance with her son, played perfectly by Pierre Lottin as a handsome, disreputable lug. Two actors depict the character of Lucas — as a boy by Garlan Erlos and as a late teen in the film’s denouement by Paul Beaurepaire — and both charmingly embody innocence and hesitation.

During the film’s pivotal scene, in which Michelle is questioned by a detective investigating Valérie’s death, Ms. Vincent imparts several mental states within seconds: certainty, duplicity, loyalty, the need to be forgiven and forgiveness, and a soupçon of dementia. Leveraging age-related mental decline as a plot device could be seen as distasteful and all credit goes to the actress for making it credible, despite the film’s inconsistencies. 

In the end, one is left with an exquisite ambiguity, which includes a dash of the sexual variety as well as narrative and moral evasiveness. Perhaps Mr. Ozon means to impute impure and murderous thoughts on viewers, because nothing we see decisively points to desire or criminality. If so, consider me complicit — and riveted.