For a film that one observer characterized as “so, so French,” “Endless Summer Syndrome” has a circuitous provenance — particularly when considering its director, Kaveh Daneshmand. 

Born at Karaj, an Iranian city about a 45-minute drive outside of Tehran, Mr. Daneshmand now calls home the “beautiful city” of Prague, having arrived in the Czech Republic at age 28. When asked by a reporter at Radio Prague International why he doesn’t return to Iran — the country has, you know, a reputation as an important cinematic center — Mr. Daneshmand responded with kid gloves: Working in his homeland is a dream, sure, but Iran is “a very problematic place.”

That’s putting it mildly, of course. Politesse seems to be Mr. Daneshmand’s forte. He goes on to mention that the film he has in development wouldn’t pass muster with Iranian authorities, and the same is true for his debut feature, “Endless Summer Syndrome.” Given the latter’s provocations — about family, parenthood, love, and betrayal — it’s a wonder anyone let him get away with it. Mr. Daneshmand is unafraid to plumb unspeakable situations. Is that what makes “Endless Summer Syndrome” French? 

Working under the auspices of production companies based in the Czech Republic and France, Mr. Daneshmand has crafted a film of uncommon assurance and unnerving portent, treading into territory that could easily have descended into the sensationalistic and lurid. He co-authored the screenplay with Laurine Bauby and based it on an idea by Gem Deger, the latter of whom also stars in the film. The story they weave is small in scope; pointed, too. Watch for sharp edges.

Welcome to the French countryside. At its center is 50-something Delfine (Sophie Colon), a lawyer and an advocate for good liberal causes. She shares a spacious manse with husband Antoine (Mathéo Capelli), an author of some notoriety and critical standing. Although we learn that his novels turn a profit, it is nonetheless clear that Delfine is the breadwinner in the family. The rambling estate, the pool, the time to pursue creative endeavors — they’re due to her financial legerdemain.

Having suffered a miscarriage early in their union, Delfine and Antoine decided on adoption to start a family. Adia (Frédérika Milano) is now 17 and brother Aslan (Mr. Deger) is a few years younger. The latter is anxious as he’s preparing for a year’s study at New York City. Antoine is convinced that his son will benefit from lessons learned while out from under parental influence.

Aslan has tasked Adia with maintaining his snail terrariums, being especially concerned with the care-and-upkeep of Stella, a snail who has been isolated in its own tank due to its venomous nature. From time to time, Mr. Daneshmand augments the film with close-ups of these creatures, as well as interrupting the timeline by shuttling us to a present in which the family members are interrogated by a local gendarme. Something significant has occurred, but just what is it that’s happened?

Toward the beginning film we watch as the telephone rings while Delfine readies herself to join Aslan, Aida, and Antoine poolside on an idyllic summer afternoon. A woman’s voice, hesitant and insistent on maintaining her anonymity, tells of Antoine’s recent night out, an evening in which he drank recklessly and became sick. Our phone caller relates how she helped Antoine after he collapsed into a drunken stupor on the floor of a public restroom. Delfine should know that Antoine, upon gaining some semblance of consciousness, confessed to having an affair with one of the children. The caller hangs up. The world is transformed.

Delfine stays mum and treads cautiously, keeping a straight face that is convincing to not one of our major players. Overcome by paranoia and disbelief, she sets up a cellphone to record her husband’s conversations on the sly. Ms. Colon gives an astonishing performance here. This is her first film and she carries it with devastating aplomb, bringing the requisite amounts of tenderness and outrage to Delfine’s character. 

“Endless Summer Syndrome” takes some shocking and explicit turns, ending on a note that would’ve made Patricia Highsmith blanch and Alfred Hitchcock green with envy. Whatever its degree of Frenchness, Mr. Daneshmand has brought us a film of impressive and unnerving power.