The ever-changing shape of things - not to mention the shape of people - which is the theme of Neil LaBute's new play, is immediately put to the test in the very theatre it is being staged in.

For in one of the more extraordinary surprises of this constantly surprising evening, the Almeida's new King's Cross performing space isn't what it seemed to be when Lulu opened it, either. The shape of this thing now has an audience seated on three sides around a wide, rectangular stage, rather than in a single steep bank in front of a deep stage.

Meanwhile, the shapes of the characters onstage appear to be mutable, too. When first seen, Paul Rudd's Adam is a nerdy, nervous art gallery attendant, sporting an ill-fitting corduroy jacket, dated haircut and glasses. In the course of the play, not only does the relationship he forges with art student Evelyn (Rachel Weisz) transform him emotionally, it also transforms him physically, both in the clothes he wears and even the nose he sports.

There's a central surprise to this relationship that makes it impossible to write about fully without giving it away; and it is simply too good to spoil. Suffice it to say that anyone familiar with LaBute's films - and in particular his first, In the Company of Men, and its brutal portrait of the moulding and manipulation of a woman by two men, will not be shocked.

But everyone who sees this should be intrigued and impressed by its brilliantly layered personality portraits that reveal how no one is what they seem or turns out the way they began. We are all of us, in any case, works in progress.

This theatrical riposte to the art installation work of Tracey Emin is hideously compelling and morbidly fascinating. And in the dazzling quartet of actors fielded in LaBute's own production, with scenes joltingly punctuated by the music of The Smashing Pumpkins, it is performed with a visceral urgency.

Rachel Weisz is the only Briton among the quartet, and the actress – who I've previously found more irritating than appealing - is at once both repellent and winning as Evelyn. Even better is Paul Rudd, at once made and manipulated by her. As the other couple, Gretchen Moll and Frederick Weller are tremendous, too, in a terrifically compelling evening.

- Mark Shenton