Twenty seconds or so into the trailer for his new film, a moustachioed Johnny Depp introduces himself: “Eigh em Lord Chally Mortdecai!” His accent is somewhere between Terry-Thomas and Inspector Clouseau; his moustache appears to have been glued on with Araldite. High camp is, it seems, the way the producers have decided to go in adapting Kyril Bonfiglioli’s sequence of novels for the big screen.

Adapting them in the first place is an idea so startlingly bizarre as to make you wonder if anyone actually read them before green-lighting the project. These four sort-of-comedy sort-of-thrillers about a cowardly and unprincipled art spiv called Charlie Mortdecai and his thuggish manservant Jock were backward-looking even when they came out in the 1970s, with their exultant snobbery, conspicuous streak of misogyny, and their backing cast of stereotypical Jews, funny-talking Chinese people, boilerish lady academics and inbred natives of the Channel Islands.

Yet here, apparently, they are – in a film starring Depp, and Gwyneth Paltrow as Mortdecai’s wife, Joanna. You can only wonder what Mortdecai or his creator would have made of the solecism “Lord Charlie Mortdecai” (he is the Hon Charlie Mortdecai in the books), let alone Paltrow’s views on nutrition and the molecular behaviour of water (a drink in which Mortdecai is notably uninterested).

Mortdecai himself, God knows, is no Depp: “I am in the prime of life, if that tells you anything, of barely average height, of sadly over-average weight and am possessed of the intriguing remains of rather flashy good looks … I like art and money and dirty jokes and drink. I am very successful. I discovered at my goodish second-rate public school that almost anyone can win a fight if he is prepared to put his thumb into the other fellow’s eye.”

What are the books – which have just been republished by Penguin – like? They are darker, stranger and more interesting than any film of them (or at least any film cleared for general release) could be. The first comparison for which people tend to reach is PG Wodehouse. Mortdecai is a debauched Bertie Wooster, and Jock a negative-energy Jeeves. Charlie is cunning where Bertie is dim; Jock is thuggish where Jeeves is urbane. But there’s also Fleming and golden-age detective fiction; and Bonfiglioli’s second wife, Margaret – editor of a memoir-cum-reader, The Mortdecai ABC, which now changes hands for north of £100 – points to a debt to Kipling. There’s a flavour of Mortdecai, to my mind, in the stylish pulp novels Julian Barnes used to write as Dan Kavanagh.

The novels are extremely funny, first of all. They deal, like Wodehouse, in sentence-by-sentence sparkle, in gestures of grand insouciance. When we first meet Mortdecai he is relaxing in his drawing room with the frame from a stolen masterpiece burning merrily in the fire. Soon after, he’s entertaining a policeman in the same room with bare insolence. His tone of address to the reader is bonhomous, conspiratorial. “Don’t you agree?” he’ll say – often after imparting some opinion about sex, crime or food with which the reader would be very hesitant indeed to agree.

But where they get really interesting is in the differences from their precursors. Wodehouse’s is essentially a ruly comic world – as are the non-comic worlds of the detective stories on whose conventions Bonfiglioli also draws. The adventures of Bertie and Jeeves, Holmes and Watson, Poirot or Miss Marple are comfortingly circumscribed by the covers of the books. Their worlds are bounded by a set of locations and conventions. The dramatis personae take their places, essentially unchanged, for the next outing. The Mortdecai Trilogy, on the other hand, is a complete mess. One minute Mortdecai is plotting to assassinate the Queen; the next he’s sparring with nubile hitwomen; the next he’s up to his ears in a Chinese heroin-smuggling operation.

You could say the essential feature of the trilogy is not what it takes from its precursors, but how thoroughly it fails to apply it. It reaches for the affectless jauntiness of Wodehouse, the cool viciousness of Fleming, in desperation and in vain. One of the things that struck me on rereading them was quite how much time Mortdecai spends crying. These books look for the reassurance of structure, certainty, a bounded world: and they spill out and over.

Near the (inconclusive) end of Don’t Point That Thing at Me, Mortdecai addresses the reader: “You must have noticed that, until now, my tangled tale has observed at least some of the unities proper to tragedy: I have not tried to relate what other people thought or did when this was outside my knowledge; I have not whisked you hither and yon without suitable transport, and I have never started a sentence with the words ‘some days later’. Each morning has witnessed the little death of a heavy drinker’s awakening and ‘each dusk a slow drawing down of blind’.” By this stage, the superficial order has collapsed: “the events which I thought I was controlling were in fact controlling me”.

That first novel just unravels. A plot that makes less and less sense as it goes on (though it makes more sense than the plots of the novels that came after) has Mortdecai crossing the US with a stolen Goya hidden in his car, in the course of which journey he accumulates at least three different sets of people who want him dead. He is frequently beaten and tortured. There is no clever resolution, no deus ex machina. He ends up back in the UK, scampering ratlike from hiding place to hiding place – shades of Richard Hannay on the run in The 39 Steps – until he is holed up in an abandoned copper mine waiting to be found and killed (while the priceless Goya mocks him from the wall of his hideout).

En route he loses Jock, abruptly and at random. As they are chased through countryside in the pitch dark Jock slips into quicksand. Charlie can’t pull him out and Jock matter-of-factly asks him for a quick dispatch:

‘Go on, me old mate. Quick. Put the leather in.’

I scrambled to my feet, aghast. Then I couldn’t bear the noises he was making any more and I stepped on the suitcase with my left foot and trod on his head with my right foot, grinding at it. He made dreadful noises but his head wouldn’t go under. I kicked at it frantically again and again, until the noises stopped, then I clawed up the suitcase and ran blindly, weeping with horror and terror and love.

At moments like that – or in the botched Satanic ritual at the centre of Something Nasty in the Woodshed – the writing in these books is right on the edge of something: the nervy comic caper plunging into an alcoholic anxiety dream. “He did go to the edge of darkness all right,” is how Margaret puts it. The sentences, one by one, may have the bright clink of ice cubes: but they’re bobbing about in something rather toxic.

Facebook Twitter Pinterest Ewan McGregor as Inspector Martland and Gwyneth Paltrow as Johanna. Photograph: Stephen Vaughan

Mortdecai is easily read as a sort of projection of Bonfiglioli himself – part wish-fulfilment, part reproach. It’s a reading encouraged, rather than otherwise, by the disclaimer at the beginning of the first book: “This is not an autobiographical novel: it is about some other portly, dissolute, immoral and middle-aged art dealer.”

Mortdecai shares his creator’s alcoholism – a telling epithet Charlie uses of one drink or another is that it “gets to you where you live very fast” – and he shares his connoisseurship. The books are full of reader-flattering art-world in-jokes, and sophisticated literary gags. The chapter-epigraphs to each book are taken from Browning, Swinburne or Wyatt, though in each case one is “a palpable forgery”. He shares, too, an unhappy relationship with his family: Charlie digs bitterly, from time to time, at “my father’s cupidity and chronic envy, my mother’s febrile regret at having married an impossible cad” and at his brother’s “crawling disgust at anyone and everything. Including himself. And especially me ... ”.

Of Bonfiglioli himself, Margaret says: “There was one very very traumatic happening in his life when he was, I think, 15 and living in Eastbourne. There was an air raid and he was supposed to go to the shelter, but he was actually skipping around in the street. But his mother and his brother were in the shelter, which got a direct hit. So he lost his mother and his younger brother at the age of 15. And his father gave him the impression that the wrong brother had died … I came to think that went very deep.”

There are considerable divergences. Mortdecai always has plenty of money, and moves with ease around the London underworld and the art galleries of Mayfair and St James’s. Bon – as everyone knew him – was penniless for most of his life. His great coup – never repeated – was to spot a Tintoretto in a local auction in 1964 and pick it up for £40. He lived in Oxford, Lancashire, Jersey and for a time Ireland – getting broker, drunker and lonelier.

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He married young after army service and had two children, but his first wife died. As an undergraduate at Balliol College, Oxford, and a single father of two, he met Margaret, who became his second wife. They had three more children and Bon sustained himself semi-successfully by dealing art and antiques through the 1960s. But at the end of that decade, he left Margaret after 10 years of marriage for another woman. That relationship foundered within five years. There followed another decade of drinking and writing; a downward slide, in the course of which he produced his other novels – the remaining Mortdecai books and a historical prequel starring a Mortdecai ancestor, All the Tea in China. Then, halfway through his sixth decade: gone. Cirrhosis of the liver got him in 1985.

As with his novels, whatever Bon’s deeper anxieties, he evinced a bright sociability on the surface. The poet Craig Raine, who knew him a little, says: “There are a million stories about Bon … Setting across a crowded party only to spill whisky on two women: ‘A Haig on both your blouses.’ He was portly, glistening with sweat, sparse hair plastered to his scalp, a great many silver rings, a silver dangle on a leather bootlace round his neck, a cross between Christopher Logue and Aleister Crowley. A down-at-heel, deposed king in exile, with an air of expensive habits. When we lunched, he knew the chef and ordered nothing on the menu. We had a pretty good bottle of wine: he quizzed the wine waiter: ‘do you still have that … ?’ They had. He ordered it.” Raine adds: “The silver dangle was dangled over my wife’s pregnant tummy to sex the baby. He was confident it was a boy. It was a girl.”

I’d like to be able to do more than speculate on the film itself, incidentally – but its publicists have spent the last two or three months not quite managing to produce a ticket to an advance screening. That’s usually the sign they know they have a stinker on their hands. If it turns out to be so – well, it’s nice to think that Bonfiglioli would probably have found that funny.

The Mortdecai Trilogy and The Great Mortdecai Moustache Mystery were reissued by Penguin last year. Mortdecai is now showing in UK cinemas.