The Lost Hero is an American fantasy-adventure novel written by Rick Riordan, based on Greek and Roman mythology.

He, along with Piper McLean, a daughter of Aphrodite, and Leo Valdez, a son of Hephaestus, is given a quest to rescue Hera, the queen of gods, from the clutches of Gaea, the primordial goddess of the earth.

It is the first book in the Camp Half-Blood chronicles to use third-person narration, switching between the points of view of Jason, Piper, and Leo.

It was named the best children's book of 2010 by Barnes & Noble and won the Junior Young Reader's Choice Award in 2013.

After they arrive there, a classmate, Dylan, turns into a storm spirit and attacks the trio and their trip leader, Coach Gleeson Hedge.

After encountering Boreas, Piper, Jason, and Leo discover that their enemies are working under orders from Gaea, the Greek primordial goddess of the Earth, to overthrow the gods.

Throughout their journey, they overcome numerous obstacles and eventually manage to save Coach Hedge, and also meet Thalia and the Hunters, who have also been looking for Percy.

Riordan says that "it was my way of letting them revisit that world in a fresh twist, but also to catch up with Percy and Annabeth and the rest of the gang from the first series".

He then signed one copy of the book and announced "that seven 'lucky demigods' will be selected in a sweepstakes to attend an exclusive one-week session at Camp Half-Blood at Bookpeople in July 2011".

Publishers Weekly gave a favorable review, stating that "Riordan's storytelling is as polished as ever, brimming with wit, action, and heart".

[18] The Seattle Times's Karen Macpherson called the Greek and Roman mix "fascinating" and also said that the "characters are interesting and well-developed, and the richly complex story has Riordan's trademark wry humor and nearly nonstop action".

Vicky Smith of Kirkus Reviews, for example, wrote that there are "far too many pages of stretched-out action, telling not showing and awkward dialogue" while believing that the novel would be enjoyed by "[d]ie-hard fans".

Anita Burkam of The Horn Book Magazine wrote in her review, "Riordan extends the franchise in a logical direction while maximizing the elements that made the first series so popular: irreverent heroes, plenty of tension-filled moments fighting monsters, and authentic classical mythology mixed in with modern life.

"[23] Carrie R. Wheadon of Common Sense Media rated it 4/5 and opined, "Percy Jackson series spin-off is almost as delightful" and observes, "The story set-up isn't terribly smooth, and this is a denser read than the first few Percy Jackson books, but once the action heats up, that's easily forgotten.

"[19] Voice of Youth Advocates comments, "The tale is longer than the Percy Jackson originals and can drag a bit at times, but fans hungry for further adventures in Riordan's modernized mythological realm will be well satisfied.

Booklist wrote that "the backstory of a master plan to unseat the gods is complex but is doled out in manageable bits with a general air of foreboding", while also appreciating "[f]lashes of humor [that] lighten the mood at times".

"[24] School Library Journal wrote that "Riordan excels at clever plot devices and at creating an urgent sense of cliff-hanging danger" and observed, "[t]he young heroes deal with issues familiar to teens today.