Polo (Apolinaris) lives in the little farm town of Karanis, far up the Nile, in the year 173 A.D. A family friend, a retired Roman officer, has written letters of recommendation for him so that he can join the Praetorian Fleet, and now he is on his way to Alexandria, on the coast of Egypt, as the first stage of his journey to Rome. But the officer included a mysterious list of names along with his letters, and someone wants it destroyed. Brigands attack Polo and his party in the desert, someone pushes him into a pool full of crocodiles, and finally a traveling companion steals the list. River pirates assault the boat carrying Polo and his friend Apion down the Nile, and elsewhere Antonius Longus - the boy who stole the list - finds that joining a conspiracy against Rome is not as simple as he thought. The three meet again in the baths of Alexandria, where an agent of the prefect of Egypt chases the conspirators and tries to reclaim the list.