The Lost Hero / The Son of Neptune (The Heroes of Olympus #1-2)

The Lost Hero
When they're attacked by strange monsters during a field trip to the Grand Canyon, Jason, Piper, and Leo are rescued by some of Percy Jackson's pals and taken to Camp Half-Blood. There, the teens discover the truth-they're demigods! But unlike the other campers, who have Greek gods and goddesses for parents, Jason, Piper, and Leo have Roman gods and goddesses for parents! Now the three are learning about their unique demigod abilities-and facing a deadly prophecy. It turns out that the goddess Hera has been kidnapped and it's up to these new demigods to save her!
The Son of Neptune
Percy Jackson has lost his memory. He knows that he's a demigod, but about the only thing he remembers from his past is a name: Annabeth. On the run from Medusa's two snake-haired sisters, Percy Jackson discovers Camp Jupiter-the West Coast camp for Roman demigods. But why is everyone looking at Percy strangely and calling him the Son of Neptune? Percy befriends two misfit campers, Frank and Hazel, and the trio soon discovers that the evil Titan Gaea has imprisoned Thanatos-aka Death-and is assembling an army of monsters to defeat the gods. Now it's up to these three teen demigods to free Death-and uncover the meaning of a mysterious prophecy about the Greek and Roman demigods.