Collins’s epistolary novel was serialized in All the Year Round before being published in book form. It effectively blends the conventions of the new and popular sensational novel of the 1860s in England, the varied points of view of the epistolary novel, and the features of the detective story. The moonstone is an Indian diamond stolen from the forehead of a statue, probably by Rachel Verinder’s evil uncle Herncastle ; this we discover from an extract from Herncastle family papers. She inherits it and wears it on her eighteenth birthday at a house party attended by all the main characters. Suspicious Indian jugglers are on the grounds. Franklin Blake, whom Rachel was assumed to love, is one of the guests, but when the stone is stolen during the night, Rachel wants nothing more to do with him.
The famous Sergeant Cuff is called in but can discover nothing. The maid Rosanna Spearman drowns herself. The Verinder family steward, Gabriel Betteredge, much enamored of using Robinson Crusoe for sortilege, narrates thus far.
During the next year, Rachel first accepts and then rejects the proposal of her cousin Godfrey Ablewhite, who was also present at the house party. She learns that he is after her money, as the evangelist and family relative Drusilla Clack tells us in the second narrative. These accounts, by the way, are requested by Franklin Blake, who after a year of traveling comes back and decides to solve the mystery. His first move is to ask Rachel, who shocks him by telling him she saw him take the diamond. Franklin enlists the aid of Ezra Jennings, the family physician’s assistant, who suggests that they reconstruct the evening of the theft, with Franklin taking the laudanum dose that the doctor, miffed at something Blake said, had secretly given him. The reconstruction merely deepens the mystery.
Mr. Bruff, the Verinder family solicitor, has the next narrative, and Ezra Jennings the last. Collins shows how the telling of a story from several points of view, explored in eighteenth and nineteenth century epistolary novels to deepen psychological insights, can be used in the detective novel to gradually reveal a mystery. And he uses to enrich the narrative the conventions that the detective story had already developed, such as the thorough but not inspired police operative versus the eccentric and socially liminal private investigator, and the solution brought together in a scene where all the principals are gathered.