The votes are in, and the award for Scariest Theatrical Prop of the Year goes to... The Pillowman.

I don't want to give too much away, but let's just say the prop in question is about seven feet tall, made of pillows, and features the deadest, most horrific smile you're ever likely to see. What's particularly chilling is that, out of all the characters in this inkily black comedy, the Pillowman himself is probably the kindest. Move over, Coraline. Those button eyes have been supplanted, and there's a new nightmare in town.

And talking of Neil Gaiman creations, there's a tangible thematic link between Martin McDonagh's Pillowman and Gaiman's Sandman story, Calliope. Both of them squarely address the idea of cruelty and torture as the wellspring of creativity. But there's a vital difference. Where Gaiman's tale of a writer who enslaves a Greek Muse to gain artificially induced talent suggests that great art is built on shameful foundations (talk about hiding in plain sight), McDonagh's play is full of characters who believe that describing acts of evil simply is great art. McDonagh's theme is the self-deception and self-absorption of writers who constantly resort to shock tactics. As such, this is an arch and elegant piece of self-mockery, as he himself resorts to shock tactics from scene one to the end.

With a less skilled writer, this would become repetitive. We start off with descriptions of axing off children's toes, and the (imaginary) gore level stays glued at max on the Tarantino Scale from that point on. But McDonagh is so earthy, so good at undercutting moments of horror with pithy putdowns, that the show twinkles with humour even at its most rebarbative. So many parents get bumped off by vengeful children in this play, it's like Roald Dahl in a really really bad mood.

The action takes place in an unnamed totalitarian state where writer Katurian K. Katurian has been arrested on suspicion of enacting some of the revolting child murders described in his fiction. With police-officers-cum-torturers Topolski and Ariel turning in one of the most gleefully sadistic good-cop-bad-cop routines of recent times, it isn't long before the truth comes tumbling out. Like Ray and Ken in McDonagh's In Bruges, these characters discuss hyperviolence in the way you and I might mention refilling the printer toner. He has a unique ability to use everyday language when describing bizarre or horrific events, and he gives it full rein here, with lines like 'The razor-blade girl was a right little shit' and 'She was just wandering around looking for lepers'.

As in her previous production Equus, director Marianne Nossair has marshalled a team of actors who rise to the challenge with style and skill. Every one of them finds that tiny sliver of space between comedy and disgust, and they probe it till it gives up its riches. Hannah Eggleton and Nate Wintraub (who seems unable to find the exit from The Pilch) are a great double-act as the police/executioners, Milo Marsh as Katurian captures that rare sensation of being the sanest man in a lunatic asylum, and Joe Rachman was born to play Katurian's disabled brother Michael. Rose Martin, Joe Baszczak and Eleanor Worth offer up deliciously disturbed cameos as mother, father and Little Jesus.

A word should also go to the sound designer Lingyi Wang, who has created a moody soundtrack of half-music, half-eerie effects which set the tone for the show. And of course, Leon Moorhouse, who created that insane, giant puppet must know he's done something remarkable. The downside for him is, I guess, that after this production is over, he'll have to keep that thing in his room.

I suspect that The Pillowman is not Martin McDonagh's greatest play. It feels almost too easy for him, like he's practising with a few leftover nasty ideas after the heights of The Lieutenant of Inishmore. It's all on one note: shocking, more shocking, then more shocking. Fortunately, even a slightly second-rank McDonagh play is top-rank entertainment. If it's not his Crime and Punishment then it's at least his Funny Games, and you couldn't ask for a grimmer fairytale than that.