In the 1799 storming of Seringapatam, India, John Herncastle, a violent and cruel man, steals the sacred Hindu diamond called the Moonstone. The jewel had been taken years before from the forehead of the Moon-God in its Brahman shrine, and Herncastle’s theft was only one of a series. Since the stone had first been stolen, three faithful Hindus followed its trail, sworn to recovering the gem and returning it to the statue of the Moon-God. Herncastle took the gem to England and now keeps it in a bank vault. He saves himself from murder by letting the Hindus know that if he were killed the stone would be cut up into smaller gems, thus losing its sacred identity. At his death, Herncastle leaves the jewel to his niece, Rachel Verinder.
The stone is to be presented to Rachel on her birthday following her uncle’s death. Young Franklin Blake, Lady Verinder’s nephew, is asked by Herncastle’s lawyer to take the gift to his cousin’s home several weeks before the event, but he barely misses death at the hands of the Hindus before reaching his destination. On the advice of Gabriel Betteredge, the Verinders’s old family servant, Franklin puts the gem in the vault of a bank nearby until the birthday arrives, as the Hindus had been seen in the neighborhood. Upon meeting, Franklin and Rachel fall in love. Guests begin to arrive for the birthday celebration, including Godfrey Ablewhite, a handsome and accomplished charity worker; Dr. Candy, the town physician; and Mr. Bruff, the family lawyer.
While the guests at the birthday dinner are admiring the beauty of the jewel, they hear the beating of a drum on the terrace and three Hindus appear, disguised as jugglers. One of the guests, Mr. Murthwaite, who had traveled widely in Asia, speaks sharply, whereupon the three men retreat. Watchdogs are released to protect the house that night. All seems well, but in the morning Rachel announces that the jewel has disappeared from an unlocked cabinet in her dressing room. Despite Rachel’s protests, Franklin Blake insists the police be called. The Hindus are arrested and put in jail, but to everyone’s astonishment, they have alibis for the entire night.
Little about the crime is discovered until Sergeant Cuff of Scotland Yard arrives. He decides that fresh paint from the door in Rachel’s dressing room must have come off on someone’s clothes. Inexplicably, Rachel refuses to allow a search for the stained clothing. Sergeant Cuff suspects that Rachel had staged the theft herself, and that Rosanna Spearman, a maid with a criminal record, is a party to the plot, for he learns that Rosanna had made a new nightdress shortly after the theft. Sergeant Cuff guesses that the nightdress was to replace another dress that is stained. Because the Verinders oppose his efforts, he drops the case. The only other clue he has is that Rosanna might have hidden something in the rocks by the seashore. Rosanna commits suicide soon afterward by throwing herself into a pool of quicksand. She leaves a letter...
(The entire section is 1227 words.)