Ludovica Bonnaire, a pampered Victorian noble, dreams of adventure. Spurred by her desire to learn more about the world outside her sheltered existence, she steals her brother's identity (along with his ship) and heads out on a journey to find love, excitement, and enough material to write a book about her favorite aquatic creatures, sea sponges. Before long, she realizes life at sea isn't as simple as the romantic novels made it seemand there are many sinister things lurking in the depths below.