Atom Egoyan is one of today’s most interesting filmmakers, with one indisputable masterpiece (“The Sweet Hereafter”) to his credit, but a variable one; and he’s made a serious misstep in adapting Anne Fontaine’s 2004 “Nathalie” to a Toronto setting.  One can understand his attraction to the material, since he’s always been drawn to stories involving peculiar sexual situations. But this time even his characteristically limpid, elegant style can’t disguise the essential silliness of the plot.

The script by Erin Cressida Wilson hews fairly closely to the original. Upscale gynecologist Catherine Stewart (Julianne Moore) suspects that her husband David (Liam Neeson), a university music professor, is having an affair after he fails to return home on time from an out-of-town lecture (and misses the surprise birthday party she’s arranged). So she hires beautiful young hooker Chloe (Amanda Seyfried), who can pass for the sort of coed she imagines him having sex with, to approach him and see if he takes the bait.

David, to be sure, is a bit of a dog, and Chloe dutifully reports that he did indeed jump at the chance she provided. She gives a graphic account of their liaisons, which sends Catherine into an emotional tailspin—not simply because of her husband’s apparent infidelity but because she finds herself lusting after Chloe and the prostitute egging on her interest. When Catherine declares her intention of breaking things off with her “employee,” Chloe goes into what can only be called Glenn Close mode. And when the good doctor confronts her husband about his dalliance with the hooker, the extent of Chloe’s machinations becomes clear.

Clearly there are some deep psychological problems in both Catherine and Chloe, in which David plays a distinctly secondary role (which Neeson, frankly, seems a mite uncomfortable with). But Wilson and Egoyan never succeed in offering even the most nebulous explanation of what they are. Thanks to Moore’s intense performance, one certainly sees the emotional toll the situation takes on her character in an exterior way, but the film doesn’t portray her inner life successfully. Chloe is an even more opaque figure, one whom Seyfried easily fills from the purely physical point of view but doesn’t make very convincing otherwise; her chilly, snarky facade makes her seem more a high school mean girl than a femme fatale.

Adding to the film’s descent into implausibility is its treatment of the Stewarts’ son Michael (Max Thieriot), a disgruntled teen who’s obliquely described as having suffered some sort of breakdown and is now inviting girls to share his bed at home. He’s also a piano prodigy who plays hockey (an unlikely combination, one would think), deeply upset over his parents’ increasing estrangement. And when Catherine breaks off with Chloe, the latter makes him a pawn in her sexual game. That leads to a finale that truly goes off the deep end and is likely to provoke more chuckles than gasps.

Egoyan handles all of this with a cool, laconic style, treating what is actually a lurid story as though it were a piece of high art, abetted by a production design (Philip Barker), art direction (Kim M. McQuister) and costumes (Debra Hanson) that make the Toronto locations a microcosm of genteel elegance. Working with cinematographer Paul Sarossy, he even gives the sex scenes a glossily attractive look, like spreads in a tony magazine. But the approach merely makes the whole thing seem more than slightly ridiculous, as though a soft-porn special were being pawned off as an important statement. Egoyan managed to handle a similarly edgy, provocative subject brilliantly in “Exotica” (1994), but here the touch eludes him. And Mychael Damma’s score doesn’t elevate the proceedings.

To be honest, “Nathalie” wasn’t any kind of great film. But its narrative conceit worked better in France than it does in Canada—even if the city had been Quebec rather than Toronto.