As the book starts, Jason Grace awakens on a school bus, unable to remember who or where he is, or anything about his past. He is sitting next to Piper McLean and Leo Valdez, who know him by name and say they are his girlfriend and best friend respectively. All three are part of a class field trip to the Grand Canyon, and after they arrive, a classmate Dylan turns into a Venti (Storm Spirit) and attacks the trio and their trip leader, Coach Gleeson Hedge. In the ensuing fight, Jason surprises everyone, including himself, when one of his coins turns into a sword which he uses to battle the storm spirits. During the fight, Coach Hedge revealed himself as a satyr and was captured by the spirits as they fled. Soon after the fight, a flying chariot appears in order to save the three, but one of the people in it, Annabeth, is upset when she discovers that her boyfriend, Percy Jackson, who mysteriously disappeared, is not there as she expected. Annabeth, seeking Percy, was told in a vision from the goddess Hera to look there for the "guy with one shoe", but this turns out to be Jason, who lost his shoe due to the storm spirit attack. Jason, Piper, and Leo are told that they are demigods and are taken back to Camp Half-Blood where they meet other Greek demigod children like themselves.