The is set in the 19th century, and it is considered the first detective story of British literature. The story has got many characters, although the most important ones are Rachel, Blake and Ablewhite and the love triangle formed among them.
The moonstone , a huge yellow diamond, is the other protagonist in the story; since it provokes all the problems and subplots in the story. As in most of Collins' stories we don't know who is the thief until the end of the story. Appearances don't seem to be what they are, and although the reader can think that the thief is Blake, we'll discover that another man with a better reputation is the guilty person.
Meanwhile, we discover step by step clues to find out the truth. Sergeant Cuff and Mr Betteredge are the best detectives to discover the mistery.
There are also grief moments in the book such as when Rosanna kills herself because she discovers that Blake doesn't love her. She also thinks that he is the person who stole the diamond , because she found some paint on his nightgown .
Ablewhite asks Rachel to marry him, she accepts but she discovers that he was only interested in her money later; so the engagement is broken.
Rachel is angry with Blake because she saw him taking the diamond the night of her birthday, but she discovers that he sleepwalked and fogives him. Someone took advantage of his state that night.
At the end Love, another basic subplot in the story, wins and Rachel finds in Blake the man she fell in love in the past. The thief was foud suffocated with his pillow by the indians. He was a gambler and had a double life.
The epilogue shows us the traveller Murthwaite and his finding the diamond in India where it should always had been.