Middle
While in Camp Half Blood Percy finds out he is with a new group of people who are very similar to him. He finds out that Camp Half Blood is where children of parents that are Greek Gods and mortal come to be safe from danger and train to defend themselves once they leave the camp. Percy is the son of Poseidon God of Water. As Percy gets acclimated to Camp Half Blood he makes some new friends. Luke Castellan, son of Hermes God of Messaging, and Annabeth Chase, daughter of Athena Goddess of Wisdom and War.
Percy also finds out that he is a very special half blood because he is the son of Poseidon one of the three eldest Greek Gods Zeus, Poseidon, and Hates. Seventy years prior to Percy's birth the three Gods made an oath to not have any more children with mortals. Percy is a clear representation that the oath has been broken. With the fact that Zeus's powerful lightning bolt has been stolen has bred much suspicion between the gods. Percy is tasked with locating that bolt before an all-out war can break out. He chooses Annabeth and Grover to accompany him on a quest to the realm of Hades, the most likely culprit. Percy is only given one week to complete this quest.
On his quest to the underworld Percy must find three crystals that are the only way on leaving the underworld. Each of them are spread out along the country being in Philadelphia, Memphis, and Las Vegas. The crystal that is in Philadelphia is guarded by medusa an evil creature when making eye contact you will turn into stone. Percy defeats this creature by using the reflection of a mirror to slice her head off and grab control of the first crystal ball.
The location of the second crystal ball is in Memphis where Percy is met by a Hydra trying very hard with his sword slicing its head off does not pay off for Percy but just ends up adding two more heads for every head chopped off. Thanks to the quick thinking of Grover he uses Medusa's head to turn the beast into cold stone and they gather up the second of three crystals needed.
The location of the third and final crystal is in Las Vegas where it is guarded inside of a casino where Percy, Annabeth, and Grover are deceived by nymphs that make them stay in the casino for three days the same amount of time it took them to get the first two crystals. Even though it takes them three days to get the third and final crystal they do prevail and head on to the entrance of Hades realm in Los Angeles.