Book 1 in the Heroes of Olyumpus series, a continuation of the Percy Jackson series. In this book, Riordan introduces the Greek Gods in their Roman aspect. Some have different names, they all have a different personalities.
Along with their different aspects, their children are also either Roman or Greek. Before this, we were rather unaware of Roman Demigods. Jason Grace is the newest demigod and is a son of Jupiter (Zeus) who has had his memory erased. He ends up in Camp Half Blood with two new Greek demigods, Piper and Leo and going on a quest with them. Then his memory slowly is given back to him. The last battle of the Percy Jackson series put the Titan king Kronos back to Tartarus, but unfortunatley, Gaea (mother earth) is not the friendly caring being we tend to think of her as in Western culture. She is the most evil of them all. Mother of the Titans, Mother to the giants she wants to help her wake fully so she can eradicate every living creature and start fresh with her tyrannical reign of power. This would mean an end to the Gods. And unfortunately, Jupiter/Zeus is very prideful. Only a demigod and God working together can overcome such enemies. But the Gods would never admit that they NEED their demigod children. Oh, and Percy has gone missing from Camp Half-Blood. Just disappeared in the night, around the same time Jason Grace turned up at the Wilderness School Piper and Leo were attending when they got picked up and taken to camp Half-Blood.
Another fun page flipping tale of mythological creatures, friendship, bravery, and loyalty.