For the past couple of weeks, the Melbourne International Comedy Festival has crashed over our fair city like a tidal wave, dragging the crowds and a bunch of increasingly exhausted critics out into the extraordinarily beautiful autumn evenings. But your humble blogger has remained at home, deaf to the siren call of comedy: far be it from me to "discourage earnest conversation," as psychiatrist Brendan Flynn suggested is the dark heritage of festival time. Flynn would approve of me: I have resolutely remained in my dour study, turning my face from the trivial levity of the light-hearted, to defend Melbourne's beetle-browed reputation as "a home of original ideas". But at least I now know who to blame for the sad state of our public discourse: it's those damn comedians.

Martin Blum as Ray Living in Welcome to Thonnet

And so it would have remained, gentle reader, had not rumours come my ears of a show called Welcome to Thonnet. Playing at the Northcote Town Hall, it is written and performed by Martin Blum. Blum is a very interesting actor: along with talents like Hayley McElhinney and Dan Spielman, he was one of the 12 original members of the STC Actors Company, resigning a couple of years later to travel overseas. The show has been assisted by various other intriguing names: its co-devisors include Chris Ryan, of Thyestes and Wild Duck fame, and Bojana Novakovic (The Story of Mary MacLane, By Herself). Govin Ruben, who's designed lighting for Hayloft and Black Lung, is production designer and provides some incidental performance. In short, all these seemed sufficient reason to wash my inky hands and venture off into the balmy night.

I returned home shaken, to recover from one of the most uncomfortably hilarious hours I have spent in the theatre. Blum is a fearless actor, and his monstrous creation, YA author Ray Living, demonstrates his courage: I haven't been on this kind of razor edge since seeing Howard Stanley's brilliant Howard Slowly shows in the 1980s. Welcome to Thonnet is pitiless: its cruelty plays on the abyss between self-perception and the perception of others that makes David Brent in the UK edition of The Office so toe-curlingly compelling.

The unassuming room in the Northcote Town Hall is a perfect setting for the show's conceit. Ray Living, unsuccessful author, has decided to attract the notice of publishers and other important people who might promote his career: and to this end he is launching his new book, Welcome to Thonnet, on the unsuspecting public. He has a lectern plastered with posters of himself and a planned evening of entertainment which includes a rendition of Greenday's Good Riddance (Time of your Life) on acoustic guitar.

He emerges from back stage with his authorial persona intact, if somewhat shakily nervous (he takes a call on his mobile because it might be, he says, from a publisher, only to find that it's his mum). He has some photographs of himself that he's happy to sign "for a gold coin donation": although they all look the same, they have "different expressions". Eager for feedback, he offers paper and pencils so the audience can note down their responses. We are given to understand that, but for the blindness of the publishing industry, we would be confronting one of the stars of teen fiction.

Even in the opening moments there's a hint of creepiness: his imagined conversation with a lonely teenager has a sweaty touch of predatoriness. The full horror doesn't really begin to dawn until he reads an extract from his first book, a scifi piece, he explains, about aliens and space ships. It's floridly pornographic, and Mr Living, all eagerness to please, is staggeringly unaware of its inappropriate nature.

Things only get worse as he turns to his new masterpiece, Welcome to Thonnet: a tale about a 17-year-old schoolboy who is (as he confesses coyly) perhaps a little like himself. The hero's name, Jay Giving, rhymes uncomfortably with Ray Living: he is a kind of pornographic Mary-Sue, a character invented by the author as a wish-fulfilment fantasy. Eventually it becomes clear that Living is a convicted paedophile, who is violating the terms of his parole.

Living's fantasies are increasingly outrageous, and he becomes at once increasingly pathetic and increasingly sinister. Blum pushes the limits of the author's self-delusion to almost unbearable heights of embarrassment. What scrapes most deeply, as it's so immediately recognisable, is Living's impregnable faith in his own talent, in the face of all the evidence against it.

Blum's performance is so convincing and detailed that, on its outing last year at the Melbourne Fringe, one reviewer seemed to take it straight, criticising Blum for his bumbling around on stage. "Awkward, why yes it was, I smiled out of tact and ended up looking at the floor to avoid feeling bad every time a bead of sweat slid down Blum’s glistening forehead." A backhanded compliment if ever there was one. Awkward it is: not because the acting is bad, but because it's so uncompromisingly good. And it's deeply, sharply funny. Not for everyone, and it comes with a strict R18+ rating: but for those who like edge on their comedy, a must see. Ends on Sunday.

Welcome to Thonnet by Martin Blum, devised with Bojana Novakovic and Chris Ryan, performed by Martin Blum, production design by Govin Ruben. Northcote Town Hall, Melbourne Comedy Festival, until April 8. Bookings.