Percy Jackson & The Olympians is a pentalogy of adventure books written by Rick Riordan, that comprises The Lightning Thief, The Sea of Monsters, The Titan's Curse, The Battle of the Labyrinth, and The Last Olympian. Interestingly, the series is set in the modern world but, as the title suggests, is also based on Greek mythology. The story begins with a twelve year old boy named Percy Jackson who discovers that he is actually the son of Poseidon, the Ancient Greek god of the sea. Percy is therefore a demigod; his father is immortal while his mother is one the latter's mortal conquests. In the process, he learns that the Olympians still exist, along with the myriad other figures, creatures and monsters from Greek mythology.
In the first book of the series, The Lightning Thief, Percy goes to a special camp for all demigods, Camp Half Blood, where most of the world's demigods live. There he learns that his dyslexia allows him to read Ancient Greek and that his attention deficit hyperactivity disorder will help him fight. Camp Half Blood offers a relatively safe environment where the demigods can train in combat to be able to kill the monsters that roam the world in the guise of human beings. The demigods also sometimes go off to complete quests; this is eventually what Percy himself does (along with his companions Annabeth Chase, another demigod, daughter of Athena, and Grover Underwood, a satyr) so as to prevent a latent war between the big three gods, Zeus, Poseidon, and Hades, over the theft of Zeus's master lighting bolt.