"The Lost Hero" is the first book in the Heroes of Olympus series by Rick Riordan. It follows three main characters: Jason Grace, Piper McLean, and Leo Valdez, who embark on a quest to rescue the goddess Hera. The story is set in a world where Greek and Roman mythology intertwine, and the characters must navigate various challenges and monsters. The narrative begins with Jason waking up with no memory of his past. As they travel, the trio discovers their unique abilities and connections to the Greek gods. The book explores themes of friendship, identity, and bravery as they confront their destinies and the dangers that lie ahead.