Joanna (Keira Knightley) and Michael (Sam Worthington) are a gorgeous, chic married couple, living in a posh New York City loft. She’s a freelance fashion writer, he’s a successful real estate agent. Half-naked much of the time, they have cute domestic squabbles and make up over midnight snacks in the kitchen. They’re at the three-year point of marriage, and a little bit uncomfortable with routine contentment—they broke up briefly during their pre-wedding courtship–but content nonetheless.

Then one night, at a party, Joanna spots Michael flirting with his co-worker, Laura (Eva Mendes). Michael is about to go on a business trip with Laura, and Joanna, understandably, is jealous. (Knightley has the most bashfully sexy smile in all of Hollywood, but even she couldn’t sport a chin mole as alluringly as Mendes). It doesn’t help that, while Michael is gone, she runs smack into her old beau, Alex (Guillaume Canet), whom she dated during her temporary split from Michael. Of course, he is French and bearded. Of course, his aching, reptilian grins, while repellent to us, still prove irresistible to her. And from that point on, director/writer Massy Tadjedin criss-crosses between Michael and Joanna’s excursions with their respective tempters, over the course of one very long night.

In other words, “Last Night” is yet another in-depth look at upper-class infidelity, another opportunity to yell “No, don’t do that!” at the screen for nearly two hours. If your facial muscles aren’t permanently sore from cringing throughout “Eyes Wide Shut,” “Closer,” “Unfaithful,” “The Last Kiss” and “The Freebie,” fear not, masochists: “Last Night” is guaranteed to provide the same level of discomfort.

Whether the affluent philanderers in these movies are swapping mates (“Closer”), taking a designated “night off” of monogamy (“The Freebie”), or banging their suburban boredom away with a worldly, hairy French stud (“Unfaithful”), their stories ultimately bear the same familiar message: no matter how scorching the siren or lothario in question, cheating is wrong, wrong, wrong. That this morality play is usually mingled with extravagantly lit, acrobatic sex scenes—that the imagery serves to glorify impulsivity while the script excoriates it—is, naturally, a paradox meant to be ignored.

To be fair, though, “Last Night” is both more implicit and less preachy than its predecessors. It’s less about adultery itself than the moments when its potential becomes overwhelmingly palpable, and Tadjedin explores rather intelligently how this generic couple might handle such urges.

She’s adept, visually, at emphasizing the characters’ jittery lust; in two separate scenes, the camera jumps downward and then rapidly back up to trail a woman’s posterior, mirroring the leering eyes of the man. Tadjedin also extracts a great deal of eroticism from the claustrophobic spaces that, at various times, enclose the two pairs—a taxi cab, a freight elevator, a shallow hotel swimming pool—without resorting to “Fatal Attraction”-like histrionics. Clint Mansell’s softly ominous piano score further heightens the guilt-ridden sexual tension.

Tadjedin, while clearly not a hedonist, is relatively forgiving, or at least understanding, of her characters’ imperfections. Happily, she doesn’t turn Alex into the aggressively seductive creep he appears to be at the outset; he’s pushy yet heartfelt, and Canet and Knightley make you believe their genuine feelings for each other. Knightley, despite looking alarmingly rail-thin—her neck is so compressed it forms a virtual Adam’s Apple—is so captivating to watch that you forgive her character’s naïve, coquettish behavior.

But the overheated lines these two have to say are straight out of third-rate soap operas (“It can’t be that kind of a night,” “I think of you when things aren’t going well,” etc). And the Mendes-Worthington interplay, while less overwrought, is just plain unconvincing. No one as effortlessly self-composed as Mendes would throw herself this shamelessly at such an indecisive, weak man. Mendes lends her unabashed sultriness to the proceedings, but her character—despite Tadjedin’s half-hearted explanation for her actions—remains underdeveloped. And the dour-faced Worthington registers more confusion than heat.

Given Tadjedin’s intimate, small-scale approach to this material, you can’t help wondering why there’s so little humor in the dialogue, and so much melodramatic stammering and brooding. Why don’t these characters ever laugh at the absurdity of what they’re doing, or even make small talk with each other? All they talk about are their urges, which only dampens the sexual fervor.

Those fascinated by certain minutiae associated with straying—the revealing body language, the nervous lip-biting, the teasing come-ons—will find “Last Night” gripping throughout. But the film will likely bore or frustrate everyone else. The libertines in the audience will want these sad-eyed fools to get on with the deed already, while the eternally faithful will just feel sorry for them.