The Countess of Morcar was a British noblewoman and the rightful owner of the Blue Carbuncle, a rare gem of exceptional value. The stone was stolen from the Countess' room at the Hotel Cosmopolitan in London, and a plumber, John Horner, was arrested on suspicion of committing the crime. The countess offered a very large reward for its return, as apart from its inherent value she maintained some sentimental attachments to the gem.