Percy, Annabeth and Thalia are driving in the car with Mrs. Jackson to a boarding school in Maine to get two new Half-Blood Nico and Bianca
Di Angelo that Grover has found. Once they are at the school they are attacked by a manticore named Dr. Thron who plays the principal.
Though the goddess Artemis and her hunters arrive to help Annabeth is then captured by Dr. Thorn. Artemis is troubled by the manticores
mention of a "Great Stirring of Monsters" and then goes off by herself to hunt an Olympus destroying monster she believes that has
returned from Tararus. She sends the halfblood and her hunters, including Bianca who just joined, to Camp Half-Blood with her twin
When they get to Camp Nico gets settled to camp life while Percy and his new horse Blackjack save a sea monster Percy names Bessie. Artemislieuntenant Zoe Nightshade starts to dream about the goddess being in grave danger. Percy then starts to have the same dreams about Annabeth. Both of them are unable to do anything about it before the Oracle somehow leaves her room and deliever Zoe a prophecy. Chiron and Zoe then organize a quest that Percy can't go on because the hunters don't want to travel with a boy. He then sneaks away with Blackjack and is almost stopped by Mr. Dionysus, the wine god.
Percy then gets to Washington D.C and notices Dr. Throns going into the National Museum of Natural History and following him using Annabeth's invisibility cap is Luke. Luke and a man called the General are there and summon a spartoi to hunt the quest group who is currently at the National Air and Space Museum. Percy gets there to warn then but they are all attacked by the Nemean Lion before they can all leave. They leave with the advise from Apollo to go to Cloudcroft, New Mexio. While there Grover begins to sense the presence of Pan, who sends the Erymanthian Boar to help them escape the spartio who caught with them. The boar carries them as far as Gila Claw, Arizona where the junkyard of the gods is at. After a encounterment with Ares and Aphrodite, the groups goes into the junkyard where Bianca tries to take a cursed statuette for Nico. Her theft awaken Talos and she ends up dying for it. The remaining people travel to the Hoover Damn and then after narrowly escaping the apartio again go to San francisco.
When they get to San Francisco Percy goes to find Nerues and learns that the monster Artemis was hunting is Bessie, the monster Percy saved, is an ophiotaurus. After meeting with Dr. Thron again Grover goes back to Camp Half-Blood with Bessie. Zoe, Percy and Thalia go to find Annabeth's father Frederick Chase to try to see if he can help them reach Mount Tamalpais which is the new location of the Titans' fortress on Mount Othrys. With Mr. Chase's car they travel to Garden of Hesperides. Zoe is hurt by the dragon Ladon while they pass through. From where Atlas once held up the sky they see Artemis now doing it. They see Annabeth in chain and larning that the General is Zoe's father. Percy takes the burden from Artemis so is friends can fight the Titan's advance guard. Artemis gets Atlas back under his burden but not before he woulds Zoe. Thalia fights Luke and he falls from a cliff and looks dead. With the help from Mr. Chase they get to the biplane he has fitted with bronze weaponry and they escape to Olympus. Zoe dies on the trip and is then turned into a star by Artemis.
Now during the winter solstice meeting the gods are finally convinced by Artemis to take action against the Titans. Thalia is also asked by Artemis to become an immortal Huntress and her acceptance is the only thing that prevent the onset of the Great Prohecy. Percy is told by his father that Luke is not dead and that he and Annabeth should get back to Camp Half-Blood, worried about their future. Before he can relax Percy is then forced to explain Bianca's death to Nico. Nico blames Percy and then a group of spario arrived to attack Percy. Nico is then banishes them to the realm of Hades. Percy then finds out Nico must be the son of Hades. Nico runs away and the only people who know about Nico's secret is Annabeth and Grove. They promise to hide this from everyone. Especially the Titan's army.