Following an incident with an escaped tiger, nineteenth-century London street urchin Jaffy Brown goes to work for Mr. Charles Jamrach, the famed importer of exotic animals, alongside Tim, a good but sometimes spitefully competitive boy. Mr. Jamrach recruits the two boys to capture a fabled dragon during the course of a three-year whaling expedition to the Dutch East Indies. They succeed in catching the reptilian beast, but when the ship's whaling venture falls short of expectations, the crew begins to regard the dragon--seething with feral power in its cage--as bad luck.