The Son of Neptune (Book #2 of The Heroes of Olympus Series) by Rick Riordan
Seven half-bloods shall answer the call, To storm or fire the world must fall. An oath to keep with a final breath, And foes bear arms to the Doors of Death. Percy is confused. When he awoke from his long sleep, he didn't know much more than his name. His brain fuzz is lingering, even after the wolf Lupa told him he is a demigod and trained him to fight with the pen/sword in his pocket. Somehow Percy manages to make it to a camp for half-bloods, despite the fact that he has to keep killing monsters along the way. But the camp doesn't ring any bells with him. The only thing he can recall from his past is another name: Annabeth Hazel is supposed to be dead. When she lived before, she didn't do a very good job of it. Sure, she was an obedient daughter, even when her mother was possessed by greed. But that was the problem — when the Voice took over her mother and commanded Hazel to use her "gift" for an evil purpose, Hazel couldn't say no. Now...