Intrigue, investigations, thievery, drugs and murder all make an appearance in Collins's classic who-done-it, The Moonstone. Published in serial form in 1868, it was inspired in part by a spectacular murder case widely reported in the early 1860s.

Collins's story revolves around a diamond stolen from a Hindu holy place. On her eighteenth birthday, Rachel Verinder receives the diamond, but by the following morning the stone has been stolen again. As the story unravels through multiple eyewitness accounts, the elderly Sergeant Cuff-with a face "sharp as a hatchet"-looks for the culprit.

One of Collins's best-loved novels, with an exciting plot moved along by deftly-drawn characters and elegant pacing, The Moonstone was also turned into a play by Collins; the play appears as an appendix to this edition.