The Son of Neptune by Rick Riordan
Percy Jackson has a huge problem: he cannot remember anything about his life. He woke up in a cave with a wolf named Lupa. Lupa taught him some basic things about being a demigod and sent him off to find the Roman demigod camp, Camp Jupiter. Percy does remember one thing, though-Annabeth. But who Annabeth is or where she is is still out of his mind. So Percy travels across the country to find the camp, battling monsters the whole way.
At camp, Percy is greeted by the Roman legion. On top of being overwhelmed by the size of the camp, Percy realises that some of the campers might turn out to be enemies. Soon he is sent on a quest-much to some of the campers' disgust-with Hazel and Frank, two other demigods. They must free the Greek god of death so the monsters will stay dead and defeat the giant sons of Gaea. With monsters, prophecies and the past all hindering their progress, with Percy, Hazel, and Frank be able to complete their quest and return home alive?
**Book 2 in The Heroes of Olympus**
Previous book: The Lost Hero
Next book: The Mark of Athena