Midshipman Edward Trefusis prepares for his second campaign on board HMS Fortune. He is disturbed by the strange news he has received about Amos Tunks, who he thought was drowned, shocked by what his uncle the rear-admiral shows him about Britain's terrible dangers and angered by what he learns about his enemy and rival. When Fortune sets sail, he soon finds himself embroiled in treachery, abduction and strange and riddling danger. At its centre is an ambiguous person, at once enemy and friend, who both threatens and saves and takes many forms. Truly in this new world, nothing is as it seems....