When I Lost It All

Sam McLaughin is.... well, not normal. He is a demigod in Gaea's Army with no idea what the campers of Camp Half-Blood, the very people he's supposed to be fighting, are like.
But when he and his 'friend' Pangaea, Gaea's daughter, meet a demigod from the other side, Sam realizes what he's been kept from his whole life.

Maybe HE'S the bad guy....