The Suspicions of Mr Whicher, By Kate Summerscale

Victorians loved "Shilling Shockers" from station bookstalls, but when a murder story is thin, a book needs padding, as with a hard railway seat.

The Constance Kent case is plump-full of interest and shouldn't need any puffing out, no matter how long the journey.

In 1860, the body of three-year-old Saville Kent was thrust into the servants' lavatory of his father's country house. Among other injuries, his throat had been slashed. The local constabulary bumbled deferentially and inconclusively, although when Inspector Whicher of the newly-formed Detective Force arrived from London, his suspicions fell on Constance, Saville's 16-year-old sister by a previous marriage. She protested her innocence, but five years later confessed to being the sole murderer, though it would have been physically difficult for her to commit it unaided.

Constance served 20 years' imprisonment, then emigrated to Australia, where she survived until 1944. In 1929, a writer investigating the case received an anonymous letter from Sydney detailing the miseries of Constance and her brother, William, in the household ruled by their stepmother, formerly their governess. She had married their father after the insanity and death of their own mother.

The case has been discussed many times, and Summerscale turns the spotlight on the detective. This would be interesting if she knew more about him, but the material is so threadbare that Whicher cannot buy a railway ticket without our being given a description of Paddington Station. Yet she omits crucial information about the ill-treatment of Constance's brother.

She therefore adds little of historical value, but what of the broader significance of the case? Several writers have made wild claims that it seriously influenced Wilkie Collins' The Moonstone. Summerscale reiterates their arguments extravagantly. As for Mary Elizabeth Braddon's celebrated bestseller, Lady Audley's Secret, Summerscale's view is that "Constance Kent was refracted into every woman in the book", but how does a girl of 16 become the origin of the tale of a bigamous wife?

Summerscale's final theory ignores an aspect of great contemporary interest. Little Saville Kent had displaced his half-brother as heir to their father's estate – precisely the sort of issue which provided plots for Dickens and Collins. But the book is well written: a smooth read that makes for a comfy journey.