The Moonstone by Wilkie Collins begins with Mr. John Herncastle stealing a mysterious yellow diamond from the statue of a sacred Indian god while fighting with the British army in India. The diamond makes it way to back England after John Herncastle returns from his tour with the British army. The sacred diamond is bestowed to a young woman, Rachel Verinder, a relative of John Herncastle, on her 18th birthday.
The man charged with transporting the diamond quickly suspects that something is amiss when he notices Indian men following him in London and at the Verinder estate. On the eve of her birthday, Rachel wears the diamond to dinner where she is proposed to by her cousin, but ends up refusing him, as she is in love with someone else.
That very night, the diamond is stolen once again and things begin to quickly escalate as people are accused of its theft, and those being accused begin to die. Rachel starts to act very strangely and the household is moved to London until the investigation is over.
The novel shifts between various people's point of view in an attempt to piece together the mystery of "who done it?" Bits and pieces of the story start to come to light and the plot twists and turns in unexpected ways until the mystery is finally solved.