In 1799, a young John Herncastle and his cousin are soldiers in the British Army. They are preparing to lay siege to an Indian palace. In the camp before their assault, stories circulate about a famous Yellow Diamond in India known as the Moonstone. The Moonstone is used to worship the moon deity, and has a curious story behind it. During the Mohammedan conquests, the Diamond was saved from pillaging, and the god Vishnu charged three Brahmin priests with watching the Diamond for all the generations of men. Later, an officer in the ranks of the Emperor of the Moguls seized the Moonstone. The Brahmins and their descendants followed the Moonstone in disguise, even as the gem passed through multiple hands. It eventually fell into possession of the Sultan of Seringapatam, the palace of which the soldiers are about to storm. The story makes only an impression on Herncastle; everyone else treats it as a fable. On the day of the assault, however, the cousin witnesses Herncastle with the Diamond-laid dagger in his hand, having most likely just killed three Indian guards in the armory. After being seen by his cousin, Herncastle is not seen for the rest of the night. The general declares that thieves are to be hanged. The cousin confronts Herncastle about what happened the previous night, to which Herncastle denies knowing anything about. The cousin concludes with saying that he feels a certain superstition about the Diamond, and that others will live to regret receiving the gem from him.
The Prologue is the only part of the “Loss of the Diamond” which is not narrated by Gabriel Betteredge. The story of the Storming of Seringapatam is extracted from a family paper, and is told from the perspective of John Herncastle’s cousin. As a matter of fact, the family paper is addressed from the cousin to his other relatives, explaining why he and Herncastle are no longer friends. Like all the other narratives, this is told in first person, and in the past tense, with the cousin looking back on events from the past.
The Storming of Seringapatam and the obtaining of the Diamond can be interpreted as an allegory to the British colonization of India. The return of the Diamond to India at the end of the story is akin to India’s eventual acquired independence (see Allegories section). The Prologue contains heavy foreshadowing for the rest of the story. Herncastle’s cousin foretells that whomever receives the gem from the Colonel will live to regret it (see Foreshadowing section). As a matter of fact, the Prologue really sets up the rest of the story; without this background, the motives of the Indian priests are not present. It gives the story depth, history, relevance, and an exotic and sinister aspect. The story of the Prologue echoes legends behind the Hope Diamond and the Orlov Diamond.