If, having shimmied your bottom to exactly the right indentation in the sand for maximum comfort, you're going to hold a book up to the sun, let its world be entirely incongruous, a pleasing contrast to its holiday context. Such was my thinking when, in the quiet glaze of the Sicilian afternoon heat, the company of The Moonstone seemed the obvious choice.

Published, in serial instalments, in 1868 and described by TS Eliot as "the first, the longest, and the best of modern English detective novels", the narrative follows the disappearance and eventual recovery of a priceless stone given to Rachel Verinder on the evening of her 18th birthday.

So far, a cosy detective story. But it is the blend of drama (occasionally melodrama) and the human aspect that makes such good use of those unhurried beach hours. It is as if the characters on the page are putting in all the effort.

The novel opens with an account, "extracted from a family paper", of how, following his participation in the storming of the Indian palace of "Seringapatam" in 1799, Sir John Herncastle, a British army officer fighting in India, came to be in the possession of a "large yellow diamond". According to his cousin, Franklin Blake, Sir John took the stone from its rightful place, "set in the forehead of the four-headed Indian god who typifies the moon'", killing the three Brahmins guarding it. Before his death, one of them vowed revenge by the stone: "The Moonstone will have its vengeance yet on you and yours!" Franklin, convinced that his cousin's motives in passing the diamond on are his own form of vengeance for being a family outcast, takes the story forward. Its legacy and legend is set. A holiday context gives it wings.

As we settle in, the story jumps forward to 1848; the diamond has been missing for two years, lost the morning after it was presented to Rachel. We learn of the appearance of three mysterious Indian jugglers at the birthday party, their presence a continued theme, hanging at the edge of the text and linking the stone back to its origins. It is at this stage that Blake takes up the editorial reins, asking that Gabriel Betteridge, the house steward of the Verinder family, places the whole story on record "in the interests of the truth". It is a charm of the novel that Collins seems to hand the narration to his characters, passing to them the responsibility of the accounts that follow.

The Moonstone is funny; sometimes self-consciously so, but it is a foible to indulge. The Robinson Crusoe-loving Betteridge is a joy. Taking firm hold of his portion of the story, making references to his favoured reading matter, his all-knowing gaze falls with distaste on members of his host household. It is, to his mind, of little surprise that the grubby case of the missing jewel should have taken place under such a roof.

Furthermore, lest our own minds should wander, Betteridge commands the reader pay due attention: "Clear your mind of the children, or the dinner, or the new bonnet, or what not … and don't I know how ready your attention is to wander when it's a book that asks for it, instead of a person?" (Comfortable in your corner of the beach, you might just be thinking about bonnets.) The formality of the style is irresistible, because you are so far from it.

In the second part of the novel, dramatically entitled "the discovery of the truth", the individual accounts begin in earnest. Collins uses the series of first-person narratives he adopted in his earlier work, The Woman in White. The effect is almost but not quite that of witness statements, as a series of characters come forward at Blake's request, their peccadilloes securing our wry smiles. In their asides they impart a sense of access to the inner confidences of the tellers.

Miss Clack, the niece of Sir John Verinder, if a satirical character, is the creation of which Collins was most proud. Fabulously self-righteous and apparently struggling against her Christian virtue even to accept payment for her account, she is instructed by Franklin to stay within the limits of her direct experience of the story of the diamond and not to offer up the wisdom of hindsight. To reinforce his role as editor, not to say curator, of the narratives, Blake appends a series of footnotes to the text. In a memorable exchange Clack takes umbrage with him within these notes, about the difficulty of narrating without providing the benefits of her insights and her natural wish to "improve" the reader. Her hindsight is eventually silenced but not before she "affectionately reminds Mr Blake that she is a Christian, and that it is, therefore quite impossible for him to offend her".

As if to reverse the narrator/suspect relationship, the light of suspicion falls on Franklin himself in the last part of the novel. An unspoken love surfaces in the story of Rosanna Spearman, a former servant within the Verinder household who nursed a hidden affection for Franklin. Seeking to protect his good name and to avoid his implication in the theft of the diamond, she changes the course of events, introducing a new direction.

It has been said of The Moonstone that the author's imperious address to the reader gets in the way of his or her enjoyment of the story. For me, being on the receiving end of energetic advice, proclamations and remonstrations, from the comfort of the beach, felt a bit like lying cosseted in bed listening to the Today programme. The effort is put in by those speaking, while the reader rests.

As the story draws to a close and we learn the true journey of the diamond, bit-part characters emerge to entertain and make revelations, against a background of the continuing presence of the Indian men in London. The conduct of an experiment, carried out by Ezra Jennings (Lady Verinder's doctor) and involving the use of opium (a further theme) permits the re-enactment of the evening of Rachel's party and the disappearance of the stone.

The selection of characters chosen to tell the story of the diamond can feel arbitrary but also gives the book its charm, spinning out the mystery. The forensic exploration is as much into "society" and human weaknesses as it is into the loss of the diamond.

An Armenian friend of mine tells me it is a habit peculiar to the English and northern Europeans to read on the beach. Really, she assures me, it should be either the beach or the book. To combine them does justice to neither. This is an interesting perspective but for me, on this second acquaintance with The Moonstone, I had the best of both worlds. I read it, for the first time, aged 15, as a set text. I chose to read it, on holiday, 20 years later, because I wanted to hear those voices again and because I had the time and the space in which to do so.