Kris Marshall was right when he said that Treats is a sneaky little play, writes Nancy Groves.

Ostensibly a drawing comedy, it starts off feeling like a sitcom, thanks to its Habitatty set and a trio of actors more familiar from the small screen than the stage.

But it's canny casting, especially in the case of Marshall, whose presence casts a shadow over proceedings long after the curtain has come down.

Typecast as the loveable oaf in My Family and Love Actually, he here plays Dave, the arrogant, bullying and potentially abusive ex-boyfriend of Ann (Billie Piper), recently replaced by her new man Patrick (Laurence Fox), when the action begins.

The play charts his efforts to force himself back into Ann's flat and life by winning over first the audience, then Patrick, and finally Ann herself. And because we are used to liking him, Marshall succeeds in doing the first very quickly.

Yes, Dave's a bastard, who openly admits to arrogance, infidelities and giving Ann a split lip after her lunch meeting with a man called Justin. But he does so with such honesty and wit - "I objected to his name!" - that we laugh along with him.

Piper's Ann comes across as a bossy, joyless prude in comparison and for the first half, it is Dave's bravado and banter with gormless Patrick that gets the laughs.

But after the interval, things take a darker edge. Suffice to say that one scene offers such a shock that the whole audience - hitherto entranced by the sight of a semi-undressed Piper - gasps, as we are forced us to assess what has gone before, and acknowledge both the warning signs and our complicity.

Playwright Christopher Hampton gives each character a scene away from the triangle where they need no longer act, and it is here that the cast give their best performances.

Those who doubted Piper's career change (and I was one of them) may well be converted by her painful portrait of a woman choosing between the safe and predicatable and the dangerous but thrilling. Meanwhile, Fox will get the quietest praise for Patrick but he creates a character who is not only essential to the plot but touching in his vulnerability.

But this is Marshall's show and with it, he takes another step away from the canned-laughter echoes of My Family.

Treats runs at Richmond Theatre until Saturday, February 17 and at the Garrick Theatre, London from Monday, February 20. Call 0870 060 6651 or visit richmondtheatre.net for tickets.