The Lost Hero

Jason, who has amnesia, has Piper and Leo as friends. All three are shocked to learn that they are the offspring of classical gods, who appear both in their Greek and in their Roman forms. They are given a quest to free Hera/Juno before the earth giants can rise to end the world. They succeed, with help from a robotic dragon, a belligerent satyr, and the huntresses of Artemis. Jason discerns that he is from a Roman camp previously unknown to the Greek Camp Half-Blood, and surmises that Percy Jackson, missing from Half-Blood, is in the Roman camp with his own memory missing.