Wiki says it's "generally considered the first detective novel." It was published in 1868.

Rachel Verinder, a young English woman, inherits a large Indian diamond on her eighteenth birthday. It is a legacy from her uncle, a corrupt British army officer who served in India. The diamond is of great religious significance as well as being extremely valuable, and three Hindu priests have dedicated their lives to recovering it.

The story has been told over and over again; the BBC serialized on radio in 2011 and is sitting at present on a TV version. Perhaps a biography of the author might interest some; seems an unhappy fellow, from his pictures, but then again he had gout and an opium addiction, which would take its toll. His later works declined in quality as his insistence on highlighting social issues increased; previously he had woven the ideas into the story with skill, but from the sound of it, he spent his later years just banging drums and gongs.