Twelve-year-old Jack Harkett is a street urchin living on the London docks. So when a merchant ship sails into port at twilight, Jack recognizes it for what it is: an opportunity. But Jack has never seen a ship quite like this one. Aside from a flock of enormous black bats that flies from its hull, there's only one living soul on board-a young stowaway named Benedict Cole. Hack and he wealthy, educated Ben have little in common. But once Jack hears Ben's hair-rising story of an ill-fated expedition-the two boys find themselves on the same side of a deadly struggle. With no one to turn to and nothing to rely on but their wits, they face a plague the likes of which London has never seen.