Temptation is the name of the game of The Jacket writer Massy Tadjedin’s quietly profound directorial debut, Last Night. The temptation of such an intriguingly sexy and good-looking cast of Keira Knightley, Sam Worthington, Eva Mendes and French actor Guillaume Canet is the film’s obvious draw, and what drives a story full of acute observations and exquisite nuances. But this slow burner, which increases in intensity and passionate purpose, really impacts after viewing, posing the thought-provoking debate of whether long-term adoration is worse than the physical act of a one-night stand?

Professional couple, Joanna (Knightley) and husband Michael Reed (Worthington) have an affluent middle-class existence and apparent marital bliss, when doubt creeps in after Joanna spots her betrothed having an intimate balcony meeting with a very attractive and flirtatious work colleague, Laura (Mendes), at a party. Suspicion fuels a marital quarrel back home, the night before Michael is due to fly out of town with Laura on business. While he is away in LA, Joanna bumps into an old flame – and seemingly the love of her prior life, Frenchman Alex who is visiting New York. Joanna is invited out to dinner with him. What seems innocent enough soon ignites her passion for Alex, and his for her. Meanwhile, with Laura around, Michael has temptation of another kind to deal.

At the start, Tadjedin fittingly captures the damaging goading and ugly atmosphere in a relationship when one partner accuses the other of wandering, and how a seemingly idyllic existence is ever ready to be threatened by outside forces at any given moment. Granted, Laura is a seductive sight, and one any attached woman can rightfully relate to in a social situation, but we never really know what Michael’s previous misdemeanours are – if any – as Tadjedin keeps her cards close to her chest.

The writer/director divides her film into a compelling double dose of intrigue that turns the viewer into a betting animal as to who will stray first, and the cagey characters add to the film’s teasing and infectious mystique. On the downside, certain situations raise blunt questioning from some supporting characters that seem a trifle erroneous at times, as does the often-wordy dialogue of either party, in an attempt to not lose control, when in real-life things would surely be different in the heat of the moment.

Nevertheless, the power of the film is in the prolonging of being proven right, and Knightley’s performance far outshines her ‘husband’ Worthington’s, in one of her finest since Antonement. Annoying ‘cat-that’s-got-the-cream’ girly giggle aside that spoils an accomplished delivery, Knightley simply oozes sexual chemistry with Canet, with Tadjedin resisting pointing out apparent signs of desire, instead keeping a tight framing on her characters, and like cinéma vérité, lets events play out. In fact, all the cast look amazing, as do the sumptuous locations Tadjedin sets each individual dilemma in, adding to the extravagant nature and allure of her first work that’s kind of reminiscent of a Woody Allen piece, but without the somber humour and philosophical nature.

Sadly, the weakest link in this provocative tale is Worthington who never really ignites the screen in quite the same way as Knightley – even opposite sexy Mendes who steals their scenes together and almost makes him appear like an uncommunicative oaf, rather than an obvious intellectual equal. This is either deliberate to allow Worthington’s average ‘man-next-door’ appeal to shine through, and paint Michael as victim of female empowerment, or that the actor who excels in ‘robotic’ mode (Avatar, Terminator) just doesn’t portray enough of a spark or depth for such a part. Looking good is the first step in this film. Projecting inner emotional turmoil is the next and is vital for the two parts of the debate to be fully composed and sustained.

Apart from the tiff at the start, Tadjedin wisely makes sure there is never a dramatic, imploding climax of the relationship, allowing doubt to fester after each infidelity, even up until the very last moment and ‘cut-short’ ending, which is very apt when, again, we are challenged to wonder whether either tormented party tells the other.

Last Night has some inquisitive ingredients to make for a tantalising film. It’s just a shame that the pleasure is lessened by its impact being more unbalanced in favour of the Laura-Alex side of the equation, as one of the players on the other side is not strong enough for us to really care if he does stray or not. In fact, cut the Michael-Laura scenes out of the equation, and Tadjedin would still have a valid exploration of seduction, infidelity and guilt. The film-maker has the beginnings of a gifted directorial career which is as exciting a future prospect as a chance meeting with an old beau any day.