While it isn’t necessary to read Riordan’s Percy Jackson and the Olympians series prior to this novel, The Lost Hero takes place afterwards so the reader will be missing some background. Since this novel focuses on three characters that are new to this world, however, it is very easy to just follow and learn along with them, while realizing that there are past relationships and nuances that you aren’t in on. The Percy Jackson series is fun, and there are only five, so they are definitely worth checking out and this book contains minor spoilers for that series, at least regarding whether certain characters lived or died (Riordan does a good job of not giving away much about the big events and twists, though).
The novel begins when Jason, one of the three new heroes, wakes on a bus, surrounded by strangers, unable to remember anything about himself. The first two students to address him are Piper, who says she is his girlfriend, and Leo, apparently his best friend. After an attack from a wind spirit, they are rescued, and introduced to a whole new supernatural world, one in which gods truly exist, and they are demigods, the offspring of a human and a Greek god. Piper and Leo are quickly claimed by their supernatural parents, though Jason isn’t. However, as confused as he is, Jason appears to have some familiarity with what is going on, recognizing the gods, the symbols, and much of the mythology, even if he keeps using the Roman rather than the Greek terms. All three are under a spell or mist – Piper and Leo have been made to believe that they know Jason while Jason’s memories have been taken. Soon after their arrival, they are given a quest to free Hera from her captors. In the process, they hope to find out what is going on with Jason and why, and Piper has her own motivations as well.