The Lost Hero

 It's the first in the "Heroes of Olympus" series, which is like a follow-up to the "Percy Jackson & the Olympians" series. The story takes place in the same world filled with Greek and Roman mythology, and it features a new group of heroes.

In "The Lost Hero," the main characters are Jason Grace, Piper McLean, and Leo Valdez. They're demigods, which means they have one parent who's a god, but they can't remember anything about their past, not even who their godly parent is. They end up at Camp Half-Blood, a safe place for demigods, where they discover their unique powers and go on a quest to rescue a missing friend, who happens to be the queen of the gods, Hera.

The book introduces Roman mythology alongside Greek mythology and brings in new challenges and enemies for the demigod heroes to face. It's a story about figuring out who you are, being a hero, and the strength of friendship.

People who enjoyed Rick Riordan's previous books love "The Lost Hero," and it continues to expand on the fascinating world of mythology he's created. The "Heroes of Olympus" series follows the adventures of these new demigods as they confront threats in both the Greek and Roman mythological realms.