Second Titan War

The Second Olympian War was a war in which the Titan Kronos attempted to exact his revenge on the Olympians for defeating him and sealing him in Tartarus. He was opposed by the Olympians and the demigods of Camp Half-Blood, including Percy Jackson. The plot of the series is a plan of Kronos, who hopes to rule the world once again by defeating the gods in the war. There were four major battles: the Attack of Camp Half-Blood, the Siege of Poseidon's Palace, and contemporaneous battles of Mount Othrys and Manhattan. It lasted approximately five years if you consider it started when Luke stole the Master Bolt and the Helm of Darkness.

The Lightning Thief
In the first book, Percy, Annabeth and Grover  embark on a quest to save Percy's mother , who is currently held hostage by Hades, and to find the Master Bolt and later, the Helm of Darkness and return them by the Solstice to prevent a war amongst the Gods. The prophecy is:

You shall go west and face the god who has turned

You shall find what was stolen and see it safely returned

You shall be betrayed by one who calls you a friend

And fail to save what matters most in the end.

The Sea of Monsters
In book two, Percy, Annabeth , Grover and Tyson sneak out of camp to help Clarisse find the Golden Fleece and bring it to camp to save Thalia's Tree, which has been poisoned by Luke. They are given this prophecy:

You shall the iron ship with warriors of bone

You shall find what you seek and make it your own

But despair for your life entombed within stone

And fail without friends to fly home alone.

The Titan's Curse
The third addition to the series sees Zoë, Thalia, Bianca, Grover and Phoebe, later jonied by Nico, Percy and Tyson embark together to save Annabeth and Artemis, whom are both being held against their will. the Oracle of Delphi gives them this prophecy:

Five shall go west to the Goddess in chains

One shall be lost in the land without rain

The Bane of Olympus shows the trail

Campers and Hunters combined prevail

The Titan's curse must one withstand

And one shall perish at a parent's hand

Battle of the Labrinth
In the fourth adventure, Grover, Percy , Annabeth and Tyson go into the Labrinth to find Daedelus and Pan. The prophecy is as follows:

You shall delve in the darkness of the endless maze,

''The dead, the traitor, and the lost one raise. ''

<p style="text-align:center;">You shall rise or fall by the ghost king's hand, 

<p style="text-align:center;">''The child of Athena's final stand. ''

<p style="text-align:center;">Destroy with a hero's final breath, 

<p style="text-align:center;">And lose a love to worse than death.

The Last Olympian
In the last of the first series, the Great Prophecy is finally revealed to Percy:

<p style="text-align:center;">A half-blood of the eldest Gods

<p style="text-align:center;">Shall reach sixteen against all odds

<p style="text-align:center;">And see the world in endless sleep

<p style="text-align:center;">The hero's soul, cursed blade shall reap

<p style="text-align:center;">A single choice shall end his days

<p style="text-align:center;">Olympus to preserve or raze

At the end of the Last Olympian, the next Great Prophecy is revealed:

<p style="text-align:center;">Seven half-bloods shall answer the call

<p style="text-align:center;">To storm or fire the world must fall

<p style="text-align:center;">An oath to keep with the final breath

<p style="text-align:center;">And foes bear arms to the Doors of Death

The Master Bolt and the Helm of Darkness
Luke Castellan, a son of Hermes was contacted in his sleep by Kronos, lord of the Titans. The nature of this encounter is unknown, but he was convinced to join Kronos' cause out of a desire for revenge. He was assigned to steal the Master Bolt, Zeus' primary weapon and the Helm of Darkness, Hades' godly weapon, in order to start a war between the gods.

On a winter camp field trip to Olympus, he made his move. While the other campers and counselors were asleep he entered the throne room and stole the Master Bolt and the Helm of Darkness, as in their arrogance, the Olympians were off guard. They later discovered the theft and went to search for the thief. Ares, son of Zeus, found Luke and fought him. According to Luke, he would have won, but underestimated his opponent and was outmatched. However, he managed to save himself by speaking in Kronos' words that if the Master Bolt was successfully stolen, there would be a full scale war. Ares was intrigued and delighted at the idea of a god-war, and spares Luke, but takes the bolt and the Helm with him. Ares later fights Percy Jackson, son of Poseidon, and Percy wins and acquires the two items.

The Golden Fleece
After his defection, Luke took control of a monster cruise ship called the Princess Andromeda, which serves as his base of operations. In order to render Camp Half-Blood defenseless and eliminate a major ally of the Olympians, he poisons Thalia's tree with the help of a spy in the camp's ranks, planning to later 'allow' Percy and Annabeth to take it and heal Thalia's tree, so Thalia, daughter of Zeus will be purged from it. He hopes to use Thalia to fulfill a prophecy made about a half-blood, child of one of the Big Three.

Luke also frames Chiron for the poisoning, causing him to be fired from the camp and be replaced by Tantalus.

At first, Clarisse daughter of Ares was sent to find the Golden Fleece. Meanwhile, Percy Jackson, along with group of allies consisting of Annabeth Chase and Percy's half-brother Tyson save Grover from the Cyclops Polyphemus.

Hermes, Luke's father, persuaded Percy, Annabeth, and Tyson to go on this quest, and told them to go onto the Princess Andromeda, hoping that Percy would meet up with Luke and convince him to stop his assault on the gods. Percy and his allies landed aboard the Princess Andromeda, not knowing of it's true nature, and were captured.

During this time, Luke told the two of his plans to use the Golden Fleece to complete Kronos' resurrection and attempts to recruit Percy and Annabeth to his cause (not willing to recruit Tyson as he reminded him of the Cyclops that captured him and Thalia years ago). The two refuse, Luke ordering his bodyguards to feed the trio to a drakon. Percy and the gang escape through a lifeboat propelled by wind canister given to him by Hermes.

Luke later intercepts Percy and his friends when they are looking for a boat that they can use to get back to camp. When he is interrogating Percy for the Fleece in front of a fountain (his army of monsters watching), Percy uses the fountain to send an Iris message, tricking Luke into revealing the fact that Chiron was framed for the poisoning, resulting in Chiron being rehired. Enraged, he ordered Percy and his friends to be killed. Percy convinces Luke to duel him, a moment both had been waiting for a long time. Luke effortlessly defeats Percy, but is prevented from killing the latter when he's knocked into the pool by a boxing glove glued to an arrow. The arrow was shot by Chiron and his family of centaurs who had just then arrived and proceeded to save them. When Percy escapes, Luke's spite and hatred for the son of Poseidon only increases.

Thalia is resurrected from her tree after the Fleece "did its magic too well". It is possible and very likely that Luke's allegiance to Kronos was affected after this. He obviously wanted Thalia to be resurrected, shown when he says to Percy that he was going to give him the Fleece after he was done using it to resurrect Kronos.

Search for the Ophiotaurus
After Thalia's resurrection, Kronos' second in command, Atlas, devised a plan to capture the Ophiotaurus, which would grant the power to destroy Olympus to whomever killed it and burned its entrails. He remembers the Prophecy and chooses Thalia to be its killer. The attack on Olympus was supposed to happen after Thalia sacrificed the Ophiotaurus.

Luke Castellan is assigned to aid Atlas with this. However, Thalia and Luke were childhood friends and romantically attracted to each other, bringing Luke hesitation to carry this mission out. Knowing this, Kronos tells Luke that if he doesn't succeed in this mission, he would be chosen to be Kronos' host and therefore suffer a fate worse than death.

Some time before his mission in the Labyrinth, Luke journeyed down to the Underworld to perfect his design as Kronos' host. Making his way to the River Styx without being spotted, Luke bathed in the waters, granting him the Curse of Achilles, which made him immune to injury, except in one particular spot.

The first time this (Luke bathing in the river Styx) is hinted is in a nightmare of Percy's, where he carries the sky in a plan to trick Annabeth into holding it after she was captured, which of course succeeded. He and Atlas later use this to their advantage by forcing a captive Artemis hold the sky in her place, and Luke is happy that Annabeth survived. He also convinces Atlas to keep Annabeth alive until Winter Solstice. It is a certainty that he bathed in the River Styx before this, as he would not have been able to hold the sky otherwise.

Luke is later seen with Atlas when he summons Skeleton Warriors to hunt down Percy Jackson.

His final appearance in The Titan's Curse is when Percy Jackson, Thalia and Zoë Nightshade, a Huntress of Artemis, arrive at the regrowing fortress of the Titans, where Artemis and Annabeth are held captive. Refusing to have to kill Thalia, Luke attempts to sway her into joining their side. Thalia refuses and the two engage in a duel. Their ferocity and power demonstrated is incredible, but Thalia ultimately wins the duel, disarming Luke and cornering him against the edge of a cliff (she claims that she was always able to beat Luke in a duel). Luke continues to goad Thalia, Annabeth begging her to spare the traitor. As Thalia and Annabeth argue over his fate, Luke attempts to use the opportunity to disarm Thalia, but she kicks him off the cliff, which causes her much guilt later on.

Although his corpse is seen by both an approaching army of monsters and Percy, it is later revealed that Luke was still alive. This is because Luke had dived into the River Styx, which made him almost invincible.

After her battle with Luke, Thalia pledges herself to Artemis (though she had previously scorned the offer), in order to stop the prophecy from coming true through her. It is possible she was also thinking of Luke when she made this decision.

Mission in the Labyrinth
Due to his failure to kill the Ophiotaurus, Kronos kept true to his word, assigning Luke as his next host. However, before Kronos would take Luke's body, the latter would aid him in planning an invasion of Camp Half-Blood using the Labyrinth, which had an entrance hidden between two rocks which Percy and Annabeth find while playing a game in Camp Half-Blood.

In order to pass the gladiatorial arena in the Labyrinth he had to assign some of his monsters to fight to the death. When we see him, he has to show the giant one more match. Then a captive Percy arrives along with Annabeth and Rachel Elizabeth Dare. As a result, the owner of the gladiatorial matches has Percy face off against three opponents, the first is easily defeated, Ethan Nakamura, who is defeated with some effort and the giant himself, whom is defeated by Percy. As a result, Luke sends his monsters after them, but they escape with the help of Quintus' hellhound, Mrs. O'Leary.

It is revealed that during this time Oceanus begins to make war with Poseidon, incapacitating him when the other gods fight Typhon tell the last battle.

Kronos' Return
When the time has come, Luke is somehow put into a trance. Two telekhines, along with Ethan Nakamura, perform a ritual to resurrect him. Percy arrives to stop the ritual, but it is too late. When Ethan pledges allegiance to Kronos, the Titan lord rises in Luke's body and is given the reforged weapon, Backbiter, his scythe with which he killed his father. However, Percy is rescued by his comrades, Rachel Elizabeth Dare who through a hair brush at him so Percy could get away and Nico di Angelo who sealing their survival by summoning a boulder over the fortress where the ritual was performed. Also saving camp half-blood by stopping him from leading the charge.

A Hero's Death
The largest part of the war, The Battle of Manhattan, Luke is completely controlled by Kronos. In this time, Percy learns that when Kronos achieves full power inside of Luke's body, he will burn through Luke's body and attain his true immortal form, which would mean any mortal that is in the vicinity will be destroyed like them looking at a god. it would then empower the other titans giving them ultimate power.

Kronos made his way to the throne room of the gods with Ethan Nakamura, destroying the city of Mount Olympus as he did so. Meanwhile Percy, Annabeth, Grover, and Thalia follow closely after. Thalia's legs are trapped under falling debris saving Annabeth from Hera's curse and the others continue on. Kronos battles them in the throne room when they arrive, but Annabeth is able to catch Luke's attention, reawakening him. But only partially.

Ethan Nakamura betrays Kronos and attacks him, unsuccessfully of course, as his sword shattered against Luke's invulnerable body. Several shards lashed back at Ethan and impale him, and he staggered to the ground. Kronos, now having an internal struggle with Luke, opens a fissure in the floor beneath Ethan, and he tumbled to his end. Kronos continues to batter the trio, getting closer to his ultimate transformation to his original self.

But Annabeth managed to coax Luke back to his own mind. Luke let Percy knock Backbiter into the hearth, leaving Luke defenseless. A beaten Annabeth gives Percy her knife, as they both realized that Luke was the true hero of the prophecy. Percy gave the knife to Luke who stabbed himself in his Achilles heel, his left shoulder.

Percy, Annabeth, and Grover looked away as there was an explosion, and Kronos' fading screams. Luke was left lying on the floor, dying. Annabeth says that he would go to Elysium and Luke replies, "Think … rebirth. Try for three times. Isles of the Blessed", Annabeth replying that he always pushed himself too hard. Then, Luke asks Annabeth if she loved him, and Annabeth replied that she thought she did but truly thought of him as a brother. Then Luke pleads to Percy to not let this happen again. With that Luke died just before the gods arrived after defeating Typhon thanks to Poseidon returning defeating Typhon. In the end he was taken away by the Fates, after being blessed by Hermes, and remembered and honored as a hero by not only Percy, Annabeth and Grover, but by all.

Aftermath

 * Percy Jackson, son of Poseidon, child of the prophecy, is given the gift of becoming a god, but declines due to his love for his friends and Annabeth, who he is finally able to tell his feelings to. He instead requests that the gods claim their children by the age of thirteen and for Camp Half-Blood to construct cabins for the minor gods and Hades, and that the peaceful Titans should be released. He was thinking of Calypso in particular, a kind, beautiful Titan that was confined because of her father Atlas, but all the other peaceful Titans were also released.
 * Grover Underwood is promoted to become a member of the Council of Cloven Elders by Dionysus, and was deemed a Lord of the Wild. From this, he gained the respect of many nature spirits and the satyrs. He also is coordinating demigod searches with more demigod children being claimed all over the world thanks to Percy's request to the gods.
 * Tyson was made a General of the Cyclopes for his bravery in leading the charge against Typhon. He was also had the choice of any weapon he wanted which was a new club to replace the one that was broken in the battle. Zeus said that they would search for the finest club that could be found. (Tyson refers to his club as a stick.)
 * Annabeth Chase, as a reward from her mother Athena, is given the opportunity to rebuild Olympus in whatever way she wants as its new architect. Ares, Aphrodite, and Apollo almost immediately ask for numerous statues of themselves everywhere. She was also in charge of the designs for the new cabins at camp.
 * Rachel Elizabeth Dare went to Camp Half-Blood and takes in the spirit of the Oracle now that the curse has been lifted as Hades' children have their own cabin and are accepted by the other gods. She immediately reveals the next Great Prophecy, but it may not come true in their lifetime (although it seems to be set in motion in The Lost Hero).
 * Jason Grace was not mentioned in Percy Jackson and the Olympians, but in the Heroes of Olympus it was discovered that he lead Camp Jupiter against Krios, destroying the Titan base, Mount Othrys. It is unknown if the Romans fought in any other battles against any other Titans.