The Lost Hero by Rick Riordan
About 557 pages
Jason doesn't remember anything before he woke up the Wilderness School's bus on their way to the Grand Canyon. Apparently, he has a girlfriend named Piper and a best friend named Leo. When a terrible storm happens, putting them all in danger, and things attack them, they are taken to Camp Half-Blood. The three friends are sent on a quest to rescue Hera who has been kidnapped and was the one to take Jason's memory. With only bits and pieces of his memory, Jason sets of with his friends to prevent evil from rising.
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