This is book 1 in the Heroes of Olympus series. This series picks up where the Percy Jackson and the Olympians series left off.
In this series we meet three teenagers who are at a Wilderness Camp for Wayward Youth. They are visiting the Grand Canyon visitors center at the south rim on the Havasupai Indian Reservation. One of the kids claims to have no memory of who he is or anything else for that matter. His two best friends claim to have months of memories together with him. Their strange and very grumpy counselor also has no idea who this kid is but suspects that he is the "special package" that the counselor has been waiting for.
In this book, we realize that there is more than one camp for the demi-gods of Olympus. The mystery and adventure is wrapped up in the revelations since the amnesiac hero, Jason, slowly unravels the mystery of himself while on a life-threatening quest with his friends, Piper and Leo.
This is a great addition/continuation of the Olympians series. Again, I think this is a wonderful way to get today's kids interested in the mythology of old.