The entire series starts with Jason. Jason has no idea who he is or where he is. Lucky for him, Piper and Leo are there on the bus with him. He is an "exchange" to combine the two camps. Percy was the other half of the exchange. After being trained by the she-wolf Lupa, Percy is chased by Gorgons to Camp Jupiter- the Latin camp. Percy is trained and goes on a quest. He is taken to Alaska to fight a giant, which Hazel, a mysterious girl who knows more about the past than the present, helped create. Will they be able to destroy the giant and prevent the wakening of Gaea? Find out by reading The Son of Neptune by Rick Riordan. But don't read it unless you've read The Lost Hero - the first book in the series.