This was Rick Riordans first truly famous book and is about Percy having to deal with the struggle of having his mom abducted into the underworld and consequently having to go on a quest to safe her. Before embarking on this quest, he not only gets acknowledged by his father who is Poseidon, but also manages to find two good friends who will play a vital role during the quest the first is Annabeth Chase who is a daughter of Athena and has been living in Camp Half Blood since she was seven as well as the satyr Grover. On his quest he faces a lot of challenges but eventually manages to not only safe his mom but also retrieves the master lightning bolt which was previously stolen by supposedly Poseidon with Percy having returned the stolen goods the crisis has been avoided and Percys Mom is saved.
During the school year which Percy still spends away from the camp in a regular high school Grover manages to get himself abducted by a cyclops. At the same the guardian tree of the Camp that used to be a daughter of Zeus but got “saved” by him and turned into a tree which now guards the borders of Camp Half Blood. However, this time it is not Percy who gets chosen for a quest, so he just goes out with Annabeth to try doing it on his own. After a while and once again way too many problems they actually find Grover and manage to safe him as well as retrieve the golden fleece. After getting back to the coast he has to face of with his now rival ex friend Luke Castelan during which he would have lost however he gets saved by the Party Ponies who are friends of Chiron who is the leader of Camp Half Blood.
After the golden Fleece from the second book is hung upon the branches of the tree that once was Thalia son of Zeus she miraculously gets retransformed into human form. The third book starts with Thalia Annabeth and Percy get driven to the school Grover is currently scouting for other Demigods. Once there they meet Nico and Bianca di Angelo who both way later turn out to be Children of Hades. However, before they can get them safely to camp they get attacked by two monsters who were hiding as teachers. There they get saved by the hunters of Artemis where immediately Bianca joins these immortal virgin hunters. After a brieve pause at camp where they leave Nico who is only 12 years old. Only shortly after they depart once more to go and search for the goddess Artemis who has disappeared. After once again a bunch of challenges they get to Mount Othrys where the Titan Atlas has tricked the goddess Artemis to hold up the sky for him. Seeing how the group can not fight an immortal Titan on their own Percy and Annabeth hold up the sky for a bit each before being able to force the weight of the sky back onto Atlas and having saved the Goddess as well.
In the fourth book it is all about an entrance of the ancient Labyrinth which has opened up in the hills near Camp Half Blood. In fear of a full-blown war from Luke Castelan who has been forging himself to become the next body of the Titan Cronos who is the bbeg from the entire series. He has been basically building an army over the past years. However, to navigate the Labyrinth the only reliable way would be to use Ariadne’s String so in order to not let an army pop up next to their home Percy Annabeth and Grover delve into the Labyrinth to try and get the string for themselves. While they are down there Grover manages to achieve the greatest things that all satyrs have been striving towards meet and find Pan the lost nature god. Here we see that he has been suffering for the past hundreds of years basically since the industrial revolution and now finally says his goodbyes and tells Grover that he is now a messenger of Pan and that the humans now have to take care of the planet themselves. However, this time their quest is not so successful while they manage to find Daedalus the original builder of the Labyrinth who has lost control over its growth however, we also find out that his life is tied to the Labyrinth. After they finally manage to make it back to camp, they have a bigger battle with the Armies of the Titans however after Daedalus gets killed by the other side the entire Labyrinth starts to crumble causing most of the Army to be stuck in the now falling apart Labyrinth.
This is the final showdown of the entire series where a large scale Army of the Titans tries to overthrow Mount Olympus which is located above the Empire State Building. While the Gods are fighting Thypon the Demigods are holding the line using a Protocol of Daedalus who had an Army of Automatons stationed there. Before going any further though we have to talk about a huge Plot Point which is the Prophecy of the Child of the great three turning sixteen it basically states that as soon as a child of the big three turns 16 they will have to make a decision which decides the future of the Olymp. Now Percy who is only days away from his sixteenth birthday. So after a couple of days of a lot of battles Luke who is now also Cronos and Percy are fighting in the Throne Room of Olymp as they are fighting Percy is loosing however Annabeth manages to break through to Luke who beggs for Annabeth to be the one to kill him which she does using the dagger that he gave her all those years ago while they were travelling to the camp together for the first time when she was only seven years old. The book ends with the Gods offering Percy to join them as a lesser god granting him immortality. However Percy declines this and instead tells the gods to accept their children as to not lead to Demigods hating their parents and revolting against them and joining the other side as Luke did in the first book.