Last Night is a thoughtful little arthouse film from writer-director Massy Tadjedin, which asks interesting questions about infidelity, relationships and resilience. After attending a cocktail party, Joanna (Keira Knightley) confronts her husband Michael (Sam Worthington) about his obvious attraction to stunning colleague Laura (Eva Mendes). Joanna is emotionally perceptive, Michael is a closed book – the issue, for her, is not whether he’s attracted to another woman; it’s whether he’s honest enough to admit to it.

Their photogenic partnership is, like their slick New York loft, full of muted shades of grey which tastefully gloss over anything awkward or inelegant. It’s not a good time for Michael to go away for a business trip but that’s exactly what he does, leaving Joanna to bump into her former flame Alex (Guillaume Canet) on the street. He’s very French, very charming, and very unconcerned that she’s now married. Cue the first of Tadjedin’s questions. What actually constitutes cheating? Agreeing to have dinner with an ex, even if there is palpable potential for infidelity?

Most of the action in this film takes place over one compressed night in uniformly chic luxury suites. Tadjedin neatly splices together Joanna and Alex’s rendezvous with Michael and Laura’s segue from seminar to swimming. This is not a film that pretends to be a modern morality tale; its strength lies in its tightly scripted dialogue and in the initial big tease: who will cheat first?

Last Night is a case study in moneyed professionals’ concept of infidelity. Be warned: the lavish lifestyles of Joanna and Michael may grate; no expense is spared in allowing them to set themselves morally and emotionally adrift. However, the consummate performances of the casts, particularly a manipulative yet vulnerable Mendes, make this a worthy and surprisingly weighty film. Knightley, with her exquisite bone structure and emotive under-bite, lifts the role of jealous wife into something else altogether, and makes Tadjedin’s screenplay moresubstantial as well as more unsettling. It’s a genuinely enjoyable if not totally memorable film that leaves you feeling like you’ve learned something about the human heart and its inexplicable hankerings.