THE OPENING SEQUENCE of Abdellatif Kechiche's complex and perceptive The Secret of the Grain is so efficient that the film's shift to slow-moving naturalism comes as a surprise. But then the French-Tunisian writer-director is planning another surprise: After viewers become used to the middle section's relaxed pace, the various plotlines are gathered together in a compellingly taut final act.

The story begins on a sightseeing boat in the none-too-scenic harbor of Sète, in southern France. Our tour guide points out the declining industries served by the port, including fishing and ship repair. Then he catches the eyes of a blonde, hands the microphone to the boat's pilot, and slips below deck with the woman. Peeved but resigned to taking over the narration, the pilot picks up the mike and notes a nearby shipyard. The camera hops to that location, where an older man is about to be told that his hours have been cut.

Everyday stuff, but essential to what happens later. The tour guide is Majid, whose chronic womanizing is central to the story's final chapter. The blonde is Madelaine, a minor player, but one who symbolizes the local establishment's relationship to the city's North African community. The older man is Tunisian-born Slimane (Habib Boufares), Majid's father, and the patriarch of a clan to which he doesn't quite belong. You might say that Slimane, who will soon be laid off from the shipyard, has also been laid off from family life.

Quiet, self-contained Slimane does keep in touch with his four children and their spouses, whose concerns are also mundane: the cost of diapers for a girl who's resisting toilet training, the hefty fines on fishermen who cast their nets in prohibited zones, and the fact that local businesses would rather hire Eastern European migrants than "Frenchmen."

By that they mean themselves. Slimane's French-born sons, Majid and Riadh, don't think of themselves as outsiders, and Slimane's extended family is ethnically diverse. (Majid's neglected wife, Julia (Alice Houri), is Russian.) But to Sète's municipal bureaucrats, with whom Slimane will soon deal, the Tunisian-rooted brood is not French at all.

On Sundays, everyone in the family except Slimane gathers at the apartment of his ex-wife and his children's mother, Souad (Bouraouïa Marzouk) for a big meal of couscous and fish. (The film's French title translates as Couscous and Mullet.) One of these meals, rendered intimately with handheld camera and mostly in closeup, is the showcase for Kechiche's neorealist mode. It's a masterly ensemble piece, but one that offers no clue as to how the movie's style will shift in its final half hour.

The kids, in-laws, and grandkids live in the same dismal high-rise apartment building, but Slimane sleeps alone in a small room in the harborside hotel run by his sometime lover, Latifa (Hatika Karaoui). The adrift man's most passionate relationship is with Latifa's 20-year-old daughter, Rym (vivacious Hafsia Herzi), who's a beauty but not a model-thin one. (That's not an idle observation: Rym's ample curves are featured in the movie's climactic sequence.)

Fired at 61, Slimane is encouraged to return to the old country. Instead, he decides to open a couscous restaurant aboard a rusting, abandoned ship. Souad will be the chef, and his children will help. But it's Rym, the most loyal of surrogate daughters, who will attempt to negotiate the permit process. She takes Slimane to City Hall for a series of frustrating, and revealing, encounters with paper-pushers (including Madelaine's husband). One official, unaware of what he's really saying, keeps noting that the health code for restaurants is "French."

Refused a permanent license, Slimane decides to have a party on his shipboard eatery that will prove the idea can work. He invites all the local officials, who happily attend. (There doesn't seem to be a lot happening in Sète.) The ship looks good and the food is delicious, but thanks to Majid, the main course goes missing. While Slimane sets out to find his philandering son, Rym attempts to save the evening.

Perhaps, though, the real obstacle to the restaurant's success is that Slimane doesn't have the strength of his own dream. It's no accident that he's mostly silent, while the film's two big speeches are delivered by Rym and Julia. The story, which is both abruptly concluded and evocatively open-ended, seems to belong to the young women, not the old man.

Tunisian-born himself, actor-turned-director Kechiche clearly knows this milieu. Yet The Secret of the Grain is not merely a mirror held up to Franco-Arab culture. The filmmaker recognizes, as his "French" characters do not, that contemporary France is a place of abundant cultures, and a variety of unpredictable admixtures. The "secret" Kechiche reveals is that neither French rules nor Arab patriarchy are adequate to govern the messy business of everyday life in a polyglot land.

THE SECRET OF THE GRAIN — 2008, 154 min; at Landmark E Street.