Transforming his appearance and stealing secret documents from the French is all in a day's work for fourteen-year-old Modo, a British secret agent. But his latest mission--to uncover the underwater mystery of something called the IctÔineo--seems impossible. There are rumors of a sea monster and a fish as big as a ship. French spies are after it, and Mr. Socrates, Modo's master, wants to find it first. Modo and his fellow secret agent, Octavia, begin their mission in New York City, then take a steamship across the North Atlantic. During the voyage, Modo uncovers an astounding secret.