Twelve-year-old Jack Harkett is a street urchin living on the London docks. So when a merchant ship sails into port at twilight, recognizes it for what it is: an opportunity. But Jack had 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. Jack and the wealthy, educated Ben have little in common. But once Jack hears Ben's hair-raising story of an ill-fated expedition to Mexico - and the strange sickness that's followed him back - 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 waits, they face a plague the likes of which London has never seen...