she belies has returned from the depths of Tartarus. Artemis sends the demigods and her hunters( which now included Bianca di Angelo because she decided to join the hunt) to Camp Half Blood with her twin brother Apollo, the Greek god of the sun, prophecy, music, and healing.
Nico, unlike his sister, settles into camp life. One day, Percy and Blackjack, a black Pegasus that has grown fond of Percy, saves a cow serpent, half cow and serpent, which Percy names Bessie. Artemis's lieutenant, Zoë Nightshade, has been having weird dreams about the goddess Artemis being in danger, while Percy is having similar dreams about Annabeth also being in danger. Both of them are unable to do anything at the moment, until the Oracle, a shriveled mummy located inside the Big House attic that could tell prophecies, somehow leaves the attic to come tell Zoë a prophecy. Chiron, the centaur, and Zoë organize a quest in order to save Artemis. When Percy realizes that he is not included, he tells the meeting that he should also go. Zoë refuses because she states she will not travel with a male camper. When they are leaving for the quest, Percy successfully sneaks away from the camp with his Pegasus Blackjack, but is almost stopped by Mr. D or Dionysus, the Greek god of
wine. When the questers arrive in Washington D. C, Percy notices Dr. Thorn, the Manticore, heading into the museum of Natural History. He follows the Manticore with a cap of invisibility into the museum. He finds Luke Castellan and a man they called the General. Percy then discovers that Luke and the General are growing skeleton warriors to hunt the quest group, who were at the National Air and Space Museum nearby. Percy runs to warn the others, but before they can leave the museum, they are attacked by the Nemean Lion. They manage to kill the Nemean Lion, flee from the museum, and with the advice of the god Apollo, travel to Cloudcroft, New Mexico. In Cloudcroft, Grover senses the presence of Pan, the Greek god of the wild, who sends the Erymanthian Boar to help them escape the skeleton warriors, who have caught up with them. The boar carries them as far as Gila Claw, Arizona, where they find themselves in the junkyard of the gods. After an encounter with Ares, the Greek god of war, and Aphrodite, the Greek goddess of love, the group enters the junkyard, Bianca tries to take a statue for her brother. Because of this, she awakens a prototype Talos, which was a giant automaton made of bronze to protect Europa in Crete from pirates and invaders, and gives her life in order to save the others. The remaining questers head toward Hoover Dam, and arrived in San Fransisco after escaping from the skeleton warriors again. Once in San Fransisco, Percy seeks out Nereus,the eldest son of Pontus, and learns that the monster that Artemis is seeking is Bessie the ophiotaurus. After their last encounter with Dr. Thorn, Grover heads back to Camp Half Blood with Bessie. Zoë, Percy, and Thalia go the find Frederick Chase, Annabeth's dad, with the hope that he will be able to assist them reach Mount Tamalpais, which is the modern location of the Titans' fortress on Mount Othrys. Frederick Chase lends them his car, and the three of them travel to Mount Tamalpais. They arrive at the Garden of Hesperides, where Zoë is wounded by the dragon Ladon, the dragon that protected the garden, while Percy and Thalia pass through. From the place that Atlas, a Titan, was supposed to be holding up the sky, they see Artemis now doing his job. Seeing Annabeth in chains and learning that Atlas is Zoë's father, Percy takes the weight of the sky from Artemis's shoulders so she could help his friends battle the Titans. Artemis manages to force Atlas back into holding the sky, but not before he seriously wounds Zoë. Thalia battles Luke, pushes him off a cliff, and he appears to be dead. Frederick Chase arrives in a biplane and helps Percy and his friends escape from Mount Tamalpais. When they arrive in a safe location, Zoë dies from the wound, and Artemis turns her into a constellation. Pegasus arrives to escort Percy and the other half bloods to Olympus. During the winter solstice meeting, Artemis finally convinces the other gods to take action against the Titans. Thalia is asked by Artemis if she would join her as a hunter. Thalia accepts the offer. Percy is told by his father, Poseidon, that Luke somehow still lives. Percy and Annabeth return to camp worried about what the future could bring. Before Percy can relax at camp, he explains the death of his sister to Nico. Nico blames Percy of the death of Bianca. When a group of skeleton warriors comes to attack Percy, Nico banishes the skeletons into the realm of Hades, and runs away. Percy realizes that Nico is the son of Hades, tells Annabeth and Grover, and the three agree to hide the fact from everyone else, especially from the Titan's army and Luke.