Commissioned as part of Canongate's series in which contemporary writers retell world myths, The Fire Gospel is a hot potato. Faber's task is to recast the Prometheus myth: it's a loose reinterpretation to say the least, as I initially read the book as a reworking of the story of the crucifixion and admired Faber's fearless secularising of Christ's death. Theo Griepenkerl (the surname is borrowed from a 19th-century German painter of Prometheus Bound) steals some previously undiscovered papyrus scrolls from a looted Iraqi museum and publishes the eyewitness account of Jesus they contain. The new "Gospel of Malchus" is highly comic, as its author is little more than a gossip and a voyeur, in spite of his conversion to Christianity. Griepenkerl's mauling at the hands of the media is punishment enough even before the fissures he has caused in the world's religions start to swallow him alive. By letting slip a humanising account of Jesus's death, he unleashes unstoppable chaos. A blackly satirical tale that incinerates the likes of The Da Vinci Code.

This startling, short book by the mercurial Michel Faber is basically The Da Vinci Code with gags - and bile. What he did for the Victorian novel in The Crimson Petal and the White (2003) - rethinking and recasting it - Faber now does for the bestselling books du jour.

Theo Griepenkerl, a pathetic, overweight academic from the Toronto Institute of Classical Studies, is visiting a looted museum in Iraq. A bomb goes off and Theo discovers, hidden inside a bas-relief sculpture, nine papyrus scrolls written in Aramaic. Theo just happens to be one of the world's leading scholars of Aramaic. It seems like a miracle: "The coincidence of finding an Aramaic memoir - to have it literally falling at his feet - at a highly dramatic moment in his life, was too astounding to ignore."

Astoundingness continues. The papyrus scrolls turn out to be a fifth gospel, an account by Malchus of the last days of Jesus. Unlike the other gospels, Malchus's is a vivid, first-hand account. Malchus was in the garden of Gethsemane; Malchus it is at the foot of the cross. Before he can say "Hallelujah, praise the Lord", Theo secures himself a publishing deal, and has an overnight sensation on his hands.

Parts of the novel consist of long quoted passages from Theo's translation of the gospel of Malchus - "I wanted to strike a balance between the no-nonsense directness of the original Aramaic and the sort of weird Elizabethan-Hebrew hybrid that people are used to from the King James". The upshot of the gospel is that Jesus was not the Messiah: he was a potent symbol, or totem, for a bunch of very determined, possibly half-crazy, drug-taking followers. And His last words on the cross were not "It is finished" but "Please, somebody, please finish me."

So far, so Da Vinci. What raises and lightens the novel is Faber's exploration of the consequences of literary fame and notoriety. First, Theo is persuaded to change his name by his publisher, Baum: "Baum had convinced him that 'Theo Griepenkerl' was a problem for customers and booksellers; the chances of somebody misspelling it in a search engine, or failing to remember it in the first place, were too high. 'Grippin' was nice and simple, yet distinctive enough to stand out in a crowded marketplace." Grippin' indeed. Theo's book begins to outsell even "the latest bestsellers about sexy criminologists, celebrity footballers, lovable drug addicts, conspiracy theories, and the national trauma of 9/11 refracted with unbearable poignancy through a literary fable about an anorexic New York teenager and her imaginary friend Kuki". But of course it's not enough for him. He becomes the classic bitter and enraged author, staying up late at night to check online Amazon reviews from saddoes like Boyd Benes from Toledo ("Save your money, this one is a big letdown"), and Arnold P Lynch ("Check out the book's ISBN number: 1+3+2 66 = 666").

Things gets better. Theo hooks up with an "alpha female" editor from his publishing house who is not only beautiful and smart, but also "genuinely au fait with the controversial provenance of John Coltrane's Stellar Regions". He's hit pay-dirt. "This is what a No 1 bestseller did for you. This is what you earned along with the money."

Finally, Faber's satire becomes farce as Theo's fame and notoriety catch up with him in shocking fashion. The book's conclusion is perhaps less compelling than everything that goes before, but Faber is an author so genuinely daring, so odd, so dark and so funny that you can forgive him, like Malchus, when he gets a little bit carried away.

 Ian Sansom's The Delegates' Choice is published by Harper Perennial. To order The Fire Gospel for £11.99 with free UK p&p call Guardian book service on 0870 836 0875 or go to guardian.co.uk/bookshop