Jason has a problem. He doesn't remember anything before waking up on a school bus holding hands with a girl. Apparently she's his girlfriend Piper, his best friend is a kid named Leo, and they're all students in the Wilderness School, a boarding school for "bad kids." What he did to end up here, Jason has no idea—except that everything seems very wrong.

Twelve-year-old Percy Jackson is about to be kicked out of boarding school...again. No matter how hard he tries, he can't seem to stay out of trouble. But can he really be expected to stand by and watch while a bully picks on his scrawny best friend? Or not defend himself against his pre-algebra teacher when she turns into a monster and tries to kill him? Of course, no one believes Percy about the monster incident; he's not even sure he believes himself.

After angering his father, Zeus, the god Apollo is cast down from Olympus. Weak and disoriented, he lands in New York City as a regular teenage boy. Now, without his godly powers, the 4,000-year-old deity must learn to survive in the modern world until he can somehow find a way to regain Zeus' favor. But Apollo has many enemies - gods, monsters, and mortals who would love to see the former Olympian permanently destroyed.

Since their mother's death, Carter and Sadie have become near strangers. While Sadie has lived with her grandparents in London, her brother has traveled the world with their father, the brilliant Egyptologist, Dr. Julius Kane. One night, Dr. Kane brings the siblings together for a "research experiment" at the British Museum, where he hopes to set things right for his family. Instead, he unleashes the Egyptian god Set, who banishes him to oblivion and forces the children to flee for their lives.

¿Qué pasaría si un día descubrieras que, en realidad, eres hijo de un dios griego que debe cumplir una misión secreta? Pues eso es lo que le sucede a Percy Jackson, que a partir de ese momento se dispone a vivir los acontecimientos más emocionantes de su vida. Expulsado de seis colegios, Percy padece dislexia y dificultades para concentrarse, o al menos ésa es la versión oficial. Objeto de burlas por inventarse historias fantásticas, ni siquiera él mismo acaba de creérselas hasta el día que los dioses del Olimpo le revelan la verdad.