Lloyd Osbourne discovers a coded message hinting at the survival of his long dead father, Samuel Lloyd Osbourne. Once fully deciphered, it leads him and Stevenson on a dangerous adventure involving torture, murder, opium smuggling, a scandal involving the late King Kalakaua and baseball gambling. They also uncover an assassination plot against President Sanfor Dole. Stevenson goes undercover as an opium addict to gather clues to unravel the smuggling trade and discover the meaning of "the Honolulu Dragon.".