This first series has 5 books and the second will have 5 books. The first book is the Lightning Thief. Then comes the Sea of Monsters. The third book is the first one in winter called Titan’s Curse. The following book is called Battle of the Labyrinth. The final book of the first series is Battle of Olympus. The second series opens with the only book with out Percy Jackson, Lost Hero. The second book Percy appears again in The Son of Neptune. The Mark of Athena is where the 7 heroes unite and go to the ancient lands. The 4th book is when Percy and Annabeth drop to Tartarus. The fifth and final one is where it all gets resolved.