The Leisure Society, Trafalgar Studios 2, London

Agyness Deyn sure knows how to wear a frock. It was, after all, in the large print of her separate metier as an ex-supermodel.

Blond-bobbed and wittily pert, she looks fabulous in the floaty minidress-cum-coat number (with one of those patterns that remind you of melting tar) and pair of fringed ankle length black leather boots that she gets to wear in The LeIsure Society, a bitingly funny comedy by the award-winning Montreal dramatist, Francois Archambault. In Bobby Theodore's superbly spry translation and in a pinch-yourself-it's-so-good production by Harry Burton, this piece hits the intimate stage of Trafalgar Studios 2 with a wonderfully cheeky knowingess and then bounds forward in faintly sod-you leaps as it dissects, with outrageous honesty and bravura wit, the tangled self-deceptions about sex and parenthood of our latterday (American) yuppies.

Deyn really knows how to act. Here she plays the 21-year-old 'fuck buddy' (their term, not mine) of John Schwab's hilarious, annoyingly sexy Mark, a recently divorced unreconstructed chauvinist shit. He's been invited to a dinner where they intend to terminate their friendship by the central couple in this wily, taut four-hander. They are Peter (whose hapless lack of true balls and faintly homosocial emulation of the dreaded Mark are all the funnier because Ed Stoppard is here so unavailingly handsome – it's the Cary Grant-in-a-fix bit, sort of) and Mary (pitch-perfect Melanie Gray, a vision of viciously miserable perfectionism in sub-fuschia. This pair are waiting to hear whether they can adopt a Chinese baby and have already bought a piano in readiness for those lessons where the new arrival will conform to racial stereotype and become a trophy prodigy for them. Trouble is that they already have a son whose offtage caterwaulings can be heard through the baby alarm and – though their sex-life is apparently more a matter of accident than design these days – Mary is pregnant. In the current job market, it would be criminal not to abort, would it not?

With her unblinking angelic gaze and her complete lack of bullshit, Deyn's wonderful fuck buddy effortlessly exposes the self-serving contradictions of the rest of the quartet as she guilelessly responds positively to the idea of a sexual threesome (the question being which two will join her in the bedroom). A lesser play would have made this character more intelligent. In this, she's clear-eyed but occluded round the edges. We hear the sounds of erotic gratification through the baby tannoy just as spangly and dinky as glass-harmonica versions of the classic piano repertoire between the scenes in his highly enjoyable and well-judged production.

Booking to 31 March, box office 020 7492 1552