While many revered directors have drifted off into retirement (e.g., Bergman) or lost whatever touch they might ever have had (e.g., Godard), septuagenarian Claude Chabrol, one of the founders of the French New Wave, continues to turn out elegantly crafted, cheekily unsettling films at a remarkable rate. “Merci pour le Chocolat” (cleverly Englished as “Nightcap”), his forty-eighth picture made in 2000, is typical of his work: less a thriller than a dark, enigmatic character study, it succeeds not by springing surprises but by gradually tightening a web of coincidences and unspoken desires before gently but powerfully revealing what we’ve long suspected. It may not be one of his very best works (check out 1969’s “Le Boucher” and 1995’s “Le Ceremonie,” for instance), but it’s still a fascinating piece.

The linchpin of the plot, adapted from the 1948 mystery novel “The Chocolate Cobweb” by Charlotte Armstrong (another of whose novels was the basis for the 1947 Claude Rains film “The Unsuspected,” while a second–1950’s “Mischief”–was made into the 1952 Marilyn Monroe flick “Don’t Bother To Knock,” and a third–1968’s “The Balloon Man” was filmed by Chabrol himself in 1970 as “La Rupture”) is Marie-Claire Muller (Isabelle Huppert), the cool, perpetually composed head of a Swiss chocolate firm. As the story opens, she’s remarrying concert pianist Andre Polonski (Jacques Dutronc), to whom she’d been wed briefly many years before. After their divorce, Andre had married Lisbeth, by whom he had a son, Guillaume (Rodolphe Pauly); but Lisbeth later died in an auto accident–while the family was visiting Marie-Claire, we will eventually learn. Now reunited, Marie-Claire and Andre appear a perfect match, though Guillaume seems somewhat sullen and withdrawn. Into this mix comes Jeanne Pollet (Anna Mouglalis), an aspiring young pianist who’s the daughter of Louise Pollet (Brigitte Catillon), a widow who’s the head of the Lausanne forensics laboratory. When Jeanne discovers that she and Guillaume had almost been accidentally switched at birth, she introduces herself to Andre and becomes his pupil, setting off some envy in Guillaume and a strange reaction in Marie-Claire. Of particular interest is the hot chocolate that she insists on preparing for everyone, a treat that Jeanne eventually takes for chemical analysis to her beau Axel (Mathieu Simonet), who works in her mother’s lab.

Where “Merci pour le Chocolat” is heading won’t come as a great surprise–Armstrong’s plots weren’t exactly strong in that respect–but it builds considerable tension through the understated suggestion of passions and enigmatic desires simmering beneath the apparently placid surface of things. And while it doesn’t directly address the mildly Marxist theme of class antagonism that Chabrol has occasionally showcased, the portrait he draws here of a bourgeois existence seething with anger and pain in the midst of opulence is quite characteristic and telling enough on its own. The cast is excellent, too. Huppert beautifully maintains an attitude of studied poise very different from her less restrained more recent turns in “The Pianist” and “8 Women,” and her final scene is wrenching; this is one case where one definitely shouldn’t bolt out while the credits are running at the close. The rest of the cast is fine as well, with Mouglalis winning as an amateur sleuth and Pauly impressive as an adolescent filled with inarticulate resentment. Chabrol’s direction, as always, is assured and frequently witty; the music is perfectly chosen, too.

“Merci pour le Chocolat” is yet another reason for viewers to express their gratitude to a wonderfully sharp and savvy filmmaker.