Zen doesn't do justice to an underrated crime novelist.

First things first. If you haven't read anything by Michael Dibdin, you should do so immediately. Dibdin, who died in 2007, was a brilliant writer. His crime novels, which star an Italian detective called Aurelio Zen, are a cut above those of just about everyone else; his literary pastiches (The Last Sherlock Holmes Story, The Dying of the Light) are impresssive; and his social satires (Dirty Tricks) are nasty and clever. Why Dibdin never became as famous as, say, Ian Rankin, has always been an unfathomable mystery to me - though now that might just happen. The BBC has put Zen on the telly (Sundays, 9pm), which means Faber can republish the 11 novels in which he appears with annoying, new, viewer-friendly covers. Rankin might like to start thinking about taking Rebus out of retirement.

Zen is played by Rufus Sewell, an actor whom some of us still remember rather too fondly - "thump, thump" goes my heart - for his portrayal of Will Ladislaw in a BBC adaptation of George Eliot's Middlemarch. I have mixed feelings about this casting. Sewell is extremely sexy - his cheekbones push at the skin on his face like a pair of knees beneath a double sheet - and he is a superb actor: he manages to make Zen seem wonderfully nonchalant and yet as wily and tenacious as a ferret. All in all, he's pretty pleasing to watch.

But is he Zen? Not really. In my mind's eye, Zen has always been rather more plump, rather more fat and rather less good looking than this. Sewell looks like he could sprint down the Via Condotti without any trouble at all, even though he almost always has a cigarette in his mouth. But Dibdin's Zen is a Venetian with a certain fondness for polenta and squid cooked in its own ink: the running would be trickier, the dark suit rather tighter about his middle. My strong feeling is that there would be the odd splodge of (rabbit or wild boar) ragù on his (skinny) tie.

As it turned out, Sewell was a mere symptom of all that was wrong with the film as a whole. The thing looks completely wonderful. The director has given it a 1960s feel, with jerky camerawork and bongos on the soundtrack, and he has made sure that every shot of Rome is dome-ridden and honey-coloured and that every woman who appears is long of limb and brown of eye. It's La dolce vita meets The Prisoner. The supporting cast - Ed Stoppard, Stanley Town­send, Ben Miles - is fantastic. The dialogue is cool. And yet . . . it just never sprang to life. Thirty minutes in and I was (whisper it) just a little bored.

The storyline started (2 January) with state corruption, which is one of several things - the others being his divorce and his lonely mama - that make the famously upright Zen so melancholic. But then it descended confusingly into something else: mountain tunnels, a feral child, a random Russian offering peremptory sex. When the closing titles finally rolled, what I felt mostly was a tremendous sense of wasted opportunity.

Two more films follow this one and we must hope that they're better. It should be so easy. With Zen, Dibdin delivered a film-maker's dream - the beauty of Italy and its dark heart, tied with a neat bow of wit (Zen is brilliantly ironic). I am moderately hopeful. In Vendetta, there were moments when you could see what the right script might do. Taken to a kidnapper's remote mountain hideaway, Zen asked the man if he couldn't just "have called in office hours"? The kidnapper laughed. "I hate to see the old traditions die out," he said, wiping his pasta bowl with a wad of bread.

The next morning, as the two of them left the house, the kidnapper held open the boot of his car. Zen walked breezily past it to the front seat. Back at the office, the case "solved" - nothing is ever really solved in Italy - Zen was praised for his work by the politicians, if not by his long-suffering boss.

What would he choose by way of a reward? Easy. His rival in love, Vincenzo Fabri (played by Stoppard), had, he noted quietly, often talked of Sicily. Wouldn't a stint there do wonders for his career? The politician gazed admiringly at Zen, who looked exactly like a crocodile that had just swallowed a small mammal.

Rachel Cooke trained as a reporter on The Sunday Times. She is now a writer at The Observer. In the 2006 British Press Awards, she was named Interviewer of the Year.

This article first appeared in the 10 January 2011 issue of the New Statesman, Here comes the squeeze