David Mamet’s plays are tough to pull off because his dialogue lacks the predictable shapeliness of traditional dramatic speech. He prefers the sort of meandering, oblique, backtracking and self-deluding conversation you might overhear in a hotel dining-room. Glengarry Glen Ross opens in a restaurant, where a handful of realtors are discussing the perils and joys of their craft. The scene culminates in one of the landmarks of American drama. Top salesman Ricky approaches a potential customer in disguise and delivers a sales pitch that sounds like a poetic meditation on destiny and existence. It’s impossible to say what darkness this little masterpiece emerged from but Christian Slater (Ricky) captures all of it, abruptly and shockingly, with laser-like precision.

Ricky’s mark is a middle-aged deadbeat named James (Daniel Ryan), whose ominous black moustache sits over his upper lip like a hearse with a puncture. James accepts Ricky’s advice to buy a plot of land but the next day he changes his mind and slopes into the real-estate office hoping for a refund. The place is swarming with cops. Burglars have broken in overnight and swiped the precious ‘leads’ (contact details of potential buyers). Every employee is under suspicion. Ricky must now pitch the deal to James all over again (‘reclose him’ in the jargon), while fending off the attentions of a twitchy detective. Slater’s enigmatic features are ideally suited to the role of the swaggering salesman whose chief strength lies in his ability to suppress every trace of weakness. His broad, handsome all-American face is offset by two darting fishy little eyes. He’s aided by his colleague Levene (Stanley Townsend), who poses as a happy customer in order to convince James that the investment is sound. The elaborate pretence is hilarious to watch as they try to hoodwink Ricky’s victim a second time, and yet the sense of panic and despair are never far from the surface.

When actors get pompous they sometimes claim that performing Mamet is like playing jazz, but here the analogy is apt. Slater and Townsend share a deliriously absurd passage of co-operative rivalry, each supplementing and complementing the other, before breaking free and delivering a solo effort which the other watches in awestruck envy. They really are like two great musicians reaching the highest pitch of their art and loving every minute of it. The effect is extraordinary. Everything in life, the show seems to suggest, is a ridiculous artifice: the patter of salesmen, the storyline of the play, the stage itself, the whole of drama. All the sliding doors of concealment and illusion are laid bare for our delighted perusal and yet the show never releases its grip on the bitter truths of its storyline. This is terrific stuff, above all from the mesmerising Slater. The only pity is that Robert Glenister, who has withdrawn, is no longer part of this great ensemble. On press night, the compacted fury of his performance matched anything else on view.

Kathy Burke directs a new play by Peep Show writer Sam Bain. It looks and feels like a sitcom. We’re halfway up a Scottish mountain where Luke, a former City whizz-kid, is discovering himself through fasting and meditation. His streetwise brother Tony arrives hoping to cadge a massive loan and pay off his gambling debts. To his horror he learns that Luke intends to take holy orders, or ‘get a monk-over’ as Tony puts it. Luke’s plan is to sell their shared flat in London and invest the proceeds in a Buddhist temple.

Enter the châtelaine of the new retreat, Tara, an Irish votary who paints herself green in deference to the Hindu goddess of redemption. Tony spots instantly that Tara is using religion as a bait to extract money from Luke and he sets about exposing her as a hypocritical gold-digger. But he fails because she’s perfectly sincere, albeit confused. Tara genuinely believes that chastity and self-denial are the route to a higher existence, and without this respect for the temptations of monasticism the play would lack any charm or emotional truth. Not that it has much subtlety. Tony, wonderfully played by Adam Deacon, gets all the best laughs. He urges the celibate lovebirds to lay on a disco in their penitent’s cell. ‘Buddha wants you to have a good time,’ he says, playing drum and bass on his portable speakers, ‘not like Jesus, nailed to a plank, giving everyone a massive downer.’ To lure his brother back to London he offers him spiritual guidance. ‘You don’t need Buddha. You need to wake up with someone else’s hand on your knob for a change.’

Some may find this superficial but it knows exactly what it wants to do. There are laughs galore and some worthwhile thoughts on the conflict between religious mania and the ties of family loyalty. A bull’s-eye.