This is considered by many to be the first detective novel. I didn't expect to like it as much as I did.
The moonstone was a large yellow diamond that had been stolen during the storming of Seringapatam (India) in 1799. Through a complicated series of events, the moonstone is given to Rachel Verinder for her 18th birthday in 1848, and it disappears the next morning. The story is told by many different narrators, beginning with Mr. Betteredge, house steward for Rachel's mother, the Lady Verinder. This sounds like it would be difficult to follow, but it actually worked really well.
This is my 19th century classic for the 2015 Back to the Classics challenge. I thoroughly enjoyed it and rate it 5 out of 5.