The Lost Hero recap

Jason, Piper, and Leo, three teens at a school for troubled kids, are pulled into a demigod's world when a field trip is attacked by storm spirits. Jason has no memory of his past; Piper believes she is his girlfriend; Leo is his supposed best friend. Taken to Camp Half-Blood, they learn they are demigods: Jason a son of the sky god with power over wind and lightning, Piper a daughter of Aphrodite with a persuasive voice, and Leo a son of Hephaestus who can wield fire. The queen of the gods, Hera, has been captured, and the sleeping earth goddess Gaea is stirring, raising giants to overthrow the gods. Sent on a quest, the three cross the country fighting monsters and free Piper's kidnapped father from a giant. They rescue Hera, but learn the truth Jason forgot: he comes from a hidden Roman demigod camp, the gods have both Greek and Roman sides, and Hera swapped Jason with the missing Percy Jackson to force the two camps to unite against Gaea.

Previously, in earlier books: In the Percy Jackson stories, a boy named Percy Jackson discovered he was a demigod, the son of the sea god Poseidon, and trained at Camp Half-Blood, a summer refuge for the mortal children of the Greek gods. Over several summers Percy and his friends, the clever Annabeth Chase, daughter of Athena, and the satyr Grover Underwood, fought to stop the Titan lord Kronos and his followers from toppling the gods. A former camper named Luke, corrupted and finally redeemed, gave his life to defeat Kronos and save Olympus. In victory Percy won a promise that the gods would acknowledge all their demigod children and honor the long-neglected minor gods. A new Great Prophecy was then spoken, warning of seven half-bloods who would face a threat greater than the Titans, and hinting that the danger to come would rise from the earth itself.

The heroes reach the ancient Wolf House in the wilderness, where Hera is imprisoned and the giant king Porphyrion is rising. Jason, Piper, and Leo battle the giant's forces and free Hera, who reveals the great secret: Jason is not Greek but Roman, a leader of a separate demigod camp called Camp Jupiter, where the gods are honored in their Roman forms. Hera erased Jason's memory and sent him to the Greek camp, while sending the Greek hero Percy Jackson, memory wiped, to the Roman camp, in a desperate scheme to make the two long-hostile camps cooperate. Gaea, the earth goddess, is awakening and raising the giants, monstrous enemies born to overthrow the gods, and she can be stopped only by seven demigods, Greek and Roman, working as one. Piper rescues her father, though his memory of the ordeal is wiped for his safety. Leo has meanwhile restored a bronze dragon and begins designing a great flying warship, the Argo II. The book ends with the friends resolving to sail west to find the Roman camp, recover Percy, and unite the two camps before Gaea can fully rise.