I can't really discuss this book without giving away snippets of its wonderfully labyrinthine plot, so if you have not yet read The Moonstone but plan to do so, may I suggest that you look away now, as the conclusion of this wonderful book retains its ability to surprise even today.
The Moonstone is so often cited as being the archetype of all detective novels that one is surprised in the first place of how little Sergeant Cuff appears in the novel, and how insignificant his role in the denouement. If one is forced to pigeon-hole this novel, then it is definitely a Sensation Novel in which a detective appears, rather than a Detective Novel with a sensational plot. However, over the course, Wilkie Collins establishes a number of the conventions of the Closed House detective novel which endure to this day.
Rachel Verinder has received The Moonstone - looted from an Indian temple - as a birthday present. However that night it is stolen, and all the inhabitants of the house are suspects for Sergeant Cuff, who has been summoned from London to replace the incompetent local police force (in this detail, there is a striking parallel with Inspector Whicher, upon whom Cuff was supposedly based, and the Road Hill House murders). Cuff is a solitary man with a melancholy face and, like so many of his successors, an eccentricity - in this case, an obsession with roses.
His suspicion falls on Rosanna Spearman, the servant with the plain face and crooked back who has been rescued by Lady Verinder from a home for women with criminal pasts. Rosanna is a genuinely interesting character as she has fallen helplessly in love with the charismatic young gentleman Franklin Blake. This unrequited infatuation across the class barrier is, as far as I am aware, quite unique in Victorian fiction, where love affairs between men and woman of differing degrees of gentility are quite common, but seldom involve the serving classes.
Eventually, Franklin Blake's quest for the hand of Rachel Verinder places the onus of revealing who had stolen The Moonstone on his head, and he is in for a shock.The denouement where Blake unlocks his memory of what happened a year ago under the influence of opium is exciting if not believable in the slightest - although as a seasoned habitue of the drug, Collins is in a better position to write about its impact than I am. However The Moonstone itself has not yet been retrieved, and indeed the final scene of novel sees a resolution which is both satisfying and subtly subversive in a colonial context.
Since writing The Woman in White several years previously, Collins writing style has improved and he is in greater control of his material. Sergeant Cuff, Rosanna Spearman and the loquacious old House-Steward Gabriel Betteredge are finely drawn, but Franklin Blake and Rachel Verinder hardly fly off the page as a romantic duo, and Godfrey Ablewhite is such a do-gooder that one wonders where's the catch. But the plot compels, it drives the book forward at a ferocious pace and it still retains a genuine ability to surprise - 150 years on, it is still a cracking good read.