"Last Night" is an account of marital trust put to the test, though it's not a habitual situation of primitive carnal delights. The picture dares to approach the sensitivity of emotional need, asking difficult questions about infidelity, submitting a disconcerting query: When it comes to wandering eyes and escalating flirtations, what's the worst offense, sex or love?

Joanna (Keira Knightley) and Michael (Sam Worthington) have been married for four years and things aren't going as well as they should. Joanna has trouble accepting Michael's sexy co-worker, Laura (Eva Mendes), fearing her husband has already cheated with the sultry woman, a charge he flatly denies. Taking off on a business trip with Laura, Michael finds himself entertaining thoughts of infidelity, with Laura doing her best to tempt the married man. For Joanna, a chance meeting with old love Alex (Guillaume Canet) returns powerful feelings of romance and regret. As the two spend the night catching up, Joanna finds herself reconsidering her life choices, wondering if she committed to the right man.

Massy Tadjedin makes her directorial debut with "Last Night," and she's picked one hell of a story to launch her filmmaking career. Though her script lacks originality, with the struggle of faithfulness the basis for countless motion pictures, Tadjedin attacks the core tension with an evocative New York City frigidity, staging the film around dinner gatherings and tastefully decorated apartments filled with self-involved people. The coldness is an intriguing way to introduce the viewer to these pokerfaced characters, establishing routine and empty social graces before dissolving sophisticated exteriors when the heat is turned up. Sumptuously shot by Peter Deming, the movie lulls the viewer in with its jazzy sway, sneaking up with its sense of location and cocktail-clinking interaction.

A character piece, "Last Night" spends the entirety of the film in a state of conversation. These characters are fairly communicative, using language to excavate and lure, hoping to uncover a morsel of honesty along the way that turns flirtation into sex, possibly love. The cast is uniformly terrific in these roles, with Worthington finally revealing something resembling a pulse after spending the last two years conquering box office charts as a plastic action figure. Tadjedin asks the actor to play the majority of the performance facially, which is Worthington's forte. His tense whir of thought and suppression of instinct is crisply communicated. Canet and Mendes make for tempting temptations, though the greatest source of life here is Knightley, who I'm slowly beginning to realize can play any emotion asked of her. Joanna represents a more disturbing plot for "Last Night," as she's not on the hunt for sexual gratification, finding herself violently moved by excitement and regret when faced with comfort and professional support she's not felt in years.

It's a long night for both couples, with Tadjedin working in a few turns along the way, keeping the movie in a realm of unnerving opportunity, distancing the sexes until intensifying urges assume command. I wouldn't describe "Last Night" as sensual, but there's a pronounced lustful vibe to help urge the feature along, generating plausible outcomes for everyone involved. If you choose this film for your date night, prepare for a most uncomfortable ride home.