While Holmes is indulging in recreational morphine, he vacations with Watson at the estate of his old school chum Reginald Musgrave. Musgrave's butler is discovered prying into an enigmatic, centuries-old family document outlining an apparently meaningless ritual. When the butler and a maid he was romantically involved with disappear, Holmes and Watson set about deciphering the ritual's meaning which they hope will lead them to a long-buried treasure.