The Suspicions of Mr Whicher (ITV1)

A thriller that loses its mystery on its way from page to screen.

You can see how the people at ITV might have been seduced by the idea of commissioning a drama based on Kate Summerscale's 2008 book, The Suspicions of Mr Whicher. Surprise bestseller? Tick. Costume drama? Tick. Gruesome murder? Tick. On paper, it's irresistible, especially when you add to the above the fact that virtually all the action takes place indoors, albeit in one rather grand house (good for the budget, too, once you've bagged the appropriate toff property). But still, the fact remains: shouldn't someone, somewhere, have pointed out - before everyone got too carried away - why such a film (Easter Monday, 9pm) would also, inevitably, be something of a damp squib?

Summerscale didn't discover the Road Hill House murder of 1860; plenty of writers before her had visited the murder of three-year-old Francis Savill Kent by his 16-year-old half-sister Constance (elements of this singular crime - the little boy was removed from his bed in the dead of night, his throat slit and his body dumped in a privy - first featured in a novel as early as 1862). What set Summerscale's work apart was her suggestion that Constance had an accomplice (her brother, William), and her focus on the detective in the case, Inspector Jonathan Whicher of the Metropolitan Police. Whicher, and his suspicions, gave the author ­licence to unpick all sorts of other things, among them the development of crime fiction and our love affair with it. Her book has its ­quietly creepy moments, but it is mostly a rich and provocative social history.

Can you pack such texture into a drama? Not easily, no. So ITV gave us the story only of the crime and its aftermath - a decision that committed a murder of its own, killing off narrative tension and nuance in one fell swoop. Yes, Savill's end was bloody and, in some ways, perplexing. The investigation that followed it, however, was relatively straightforward: Mr Whicher came down to Wiltshire from London, where he soon realised that the most likely culprit was Constance, who had sought warped revenge on her stepmother by taking from her the son that she loved. Admittedly, he was unable to prove this - her bloody nightgown, a key piece of evidence, was missing and never found - and Constance remained a free woman until, in 1865, she confessed to the murder to a priest. But she was tried and convicted in the end. Mr Whicher was right.

On screen, the result was a tale that felt painfully slight and stretched, red herrings being distinctly thin on the ground. This was a pity, because in every other respect the film was superb. It captured beautifully the sense of a house that was full of dirty secrets - hallways and rooms were mostly bare, as if only recently abandoned, their inhabitants having rushed to hide themselves behind closed doors elsewhere - and the production was exquisitely restrained, mercifully free of histrionics and incidental music. The casting was very fine. Paddy Considine was absolutely my idea of Mr Whicher: plain-speaking, sincere and clever, but a touch inarticulate, as well. Considine, with his pale open face, dimpled chin and lank, schoolboy hair, can do confounded like no one else. I also loved William Beck as his bug-eyed sidekick, Dolly, aka Sergeant Williamson. Emma Fielding, as the evil stepmother, sounded to my ears too modern in her inflections, but Peter Capaldi as her hypocrite of a husband was a marvel: you never knew where you stood with him, which is exactly how Jonathan Whicher must have felt. Kent's much-vaunted openness - "You must do as you see fit, Mr Whicher" - was a gauntlet, thrown down; a deception all of its own.

I even delighted in the script, which was punctuated with the tiny hesitations of Victorian propriety. At one point, Mr Whicher asked what the bloodied piece of cloth he held in his hands actually was. "It's a garment women wear between their . . . bosom and their corset," he was told. The pause before the word "bosom" was delicious: a reminder of how much more mysterious mysteries were in the days when people had more secrets than clothes. Nevertheless, as the titles rolled, I couldn't help feeling robbed. In the end, the film was rather like its hero, poor old Mr Whicher: an honourable failure, but a failure all the same. l