The book opens up with Percy driving with Rachel Dare. His friend Charles Beckendork from Camp comes and tells him that Luke is near
and they head off to attack Princess Andromeda. Kronos, who is possesing Luke's body, isn't caught off that there is a spy at Camp
Half-Blood and Charles is killed. Percy wakes up in his father's underwater palace which is being taken over by the Titan Oceanus.
Percy wants to stay and fight but his father sends him back to Camp alf-Blood to hear the Great Prophecy.". Once Percy gets to
Camp Half-Blood, he tells everyone of the spy and learns the Gods and Goddesses are occupied fighting Typhon. Later that night
Percy leaves again with Nico, the son of Hades, to go follow a lead on Kronons. They visit Luke's mother in Westport, Connecticut
and talk to Hestia, Percy gets a blessing from his mother. He then goes to the Underworld to bathe in the River Styx and takes on
the curse of Achilles. After being beytrayed by Nico for information on his mother, Percy uses his new invulnerabilty and defeats
a army of Hades minions.
Percy goes back to New York City after coming out of the underworld and leaves Nico behind for him to convince Hades to join the fight against Kronos. Percy calls the campers to come and help defend Olympus as the gods refuse to end their fight with Typhon. Just before the fight starts New York City is put under a powerful sleeping spell from Morpheus, Hecate and Kronos. Although they had Thalia and her hunters of Artemis, the Party Poines and a few other people to help, the Olympian army struggles to fight back against the Titans. Camp Half-Blood suffers 16 deaths out of 40 campers. Annabeth is hurt badly when she saves Percy from an attack by Ethan Nakamura that would've hit Percy in his Achilles point. Even with these setback Percy still refuses to surrender and gives the gift of Pandora's pithos to Hestia. The campers defeat Hyperion and Kronos gets more angry.
Rachel Dare who has begin to have visions of a prophecy, comes to warns Percy of a deadly drakon that can only be killed by a child of Ares and that he is not the hero. The campers do poorly against the enemy until Silena Beauregard, the daughter of Aphrodite, comes disguised as Are's head counselor Clarisse and breaks down the cabin's boycott of the war. The real Clarisse comes later, anry and kills the darkon herself. As Silena is dying everyone learns that she was the spy for Kronos but she decided to do what's right after her boyfriend, Charles, died.
Percy calls his father through Iris message and explains that Kronos is playing on the gods and their children being divided. Poseidon agrees with Percy after fighting for a moment. The campers go back to the blocks that are surronding the Empire State Building. They make their last stand to protect Mount Olympus. Soon Hades arrives with Nico and an army, Kronos still manages to get into Olympus. Percy attacks Kronos without no one from either side joing in. The campers get an Iris Message and they can see Typhone getting close to New York, only to be killed by Poseidon and his clyclopes. Ethan Nakamura also rebels against Kronos but is killed. When Kronos attacks Annabeth, Luke gets control of his body and with help from Percy he hurts him at his mortal point and banishes Kronos to the void. As Luke dies he tells Percy that Ethan always had the right idea. It was unclaimed kids and unrecongnized gods that made the war start. He dies in peace and the Fates take his body away.
The gods grant a reward to the seven heroes who were the biggest help in defeating the Titans. Thalia, Grover, Annabeth, Tyson, Clarisse, Nico and Percy. When Percy is called up Zeus offers him a chances to become an immortal god. Much to the gods shock Percy declines and asks the gods to swear on the River Styx that the will claim all demigods by the time they turn thirteen, have cabins, thrones built for all minor gods and Hades and give amnesty to the innocent Titans and their former allies. Percy also relieves Zeus, Poseidon and Hades of their oath to not have demigod children. After the meetng Percy discovers Rachel's plans to become the new Oracle. He rushes to camp with Nico and Annabeth. He fears that a curse was put on the Oracle's spirt by Hades in revenege for Zeus killing Nico's mother is still there. With Apollo watching, Rachel becomes the new Oracle and tells the next Great Prophecy.
Seven half-bloods shall answer the call.
To storm or fire, the world must fall.
An oath to keep with the final breath,
As foes bear arms to the Doors of Death.
The Book ends two weeks after Annabeth celebrates Percy's sixteenth birthday and the two begin to date. (Finally!). The gods are keeping to their new promises and Camp Half-Blood returns to normal. The fallen demigods are honored at the end of the summer with the new beads.