Content Warning: This section of the guide describes and discusses references to death by suicide and Victorian-era prejudices surrounding Indian religion and culture that appear in the source text.

The Prologue is narrated by an unnamed first-person narrator, who describes events that took place in 1799 in India. The narrator writes to explain, “the motive which has induced me to refuse the right hand of friendship to my cousin, John Herncastle” (3). The narrator and Herncastle both served in the British army and participated in an attack on Seringapatam (a city in India). Before the attack, the British soldiers gossiped about famous treasures rumored to be found in the city, including a large yellow diamond nicknamed “the Moonstone.” According to legend, the Moonstone has been guarded by a succession of priests for centuries, and anyone who tries to seize the gem is cursed.

Herncastle boasted that he would get his hands on the diamond, although no one else believed him. During the fighting, the narrator happened upon Herncastle in a heavily fortified room near the palace. Two Indian men were dead nearby, and a third was dying; Herncastle was holding a bloody dagger. The dying Indian man pronounced that Herncastle and his family would suffer due to the Moonstone’s curse.