The Donmar is such an intimate theatre that almost everything turns into a real theatrical experience. When the actors are so close you can almost smell their breath, every play starts with a built-in advantage. But The Cryptogram left me feeling a bit dissatisfied. When the whole play is over in exactly an hour, one wonders whether it should have been staged as one half of a double bill, just to give the audience more of a square deal. David Mamet's short play, true to its title, leaves a lot of questions unanswered. As in many 60- or 90-minute plays I've seen in the last couple of years, the playwright leads us into what seems like a convincing setup, puts down his pen at what should be the interval, and decides that's the end of the play. That's why Edward Albee's The Goat is a much slighter work than Who's Afraid of Virginia Woolf, and Tennessee Williams' Suddenly Last Summer isn't a patch on A Streetcar Named Desire. Here Mamet provides us with a series of scenes between three characters set in 1950s America. There's a mother, Donny, her son John and her absent husband's friend Del. As in a Pinter play, we get lots of glimpses, subtexts and hints at what's going on below the surface. There is not one McGuffin but several -- a hunting knife, a torn blanket and a teapot that breaks off stage with a big crash. Josie Rourke takes the play at a cracking pace, with no Pinteresque pauses. This may be the way Mamet wanted it, but I kept on wanting the cast to slow down and explore the silences between the lines. Kim Cattrall and Douglas Henshall give fine performances as the mother and the dodgy friend who appears to have seduced her husband. The real astonishment comes from the performance of Oliver Coopersmith, one of three boys alternating in the part of John. His timing is faultless in a series of rat-tat-tat dialogues which would leave many experienced adult actors struggling.