The House of Hades is the fourth in the five-book Heroes of Olympus series that follows seven Roman and Greek demigods trying to stop the earth goddess Gaea from rising: Percy Jackson, Annabeth Chase, Jason Grace, Piper McClean, Hazel Levesque, Frank Zhang, and Leo Valdez. The series follows the events of the Percy Jackson series where he learns he is the son of Poseidon and defeats Kronos in the second Titan War.

The Lost Hero follows Jason, Piper, and Leo. They are rescued from monsters by Annabeth, who is looking for a vanished Percy, and taken to Camp Half-Blood where they learn they are demigods. Piper is Aphrodite’s daughter, Leo is Hephaestus’s son, but Jason is a Roman demigod and a son of Jupiter. His memory was wiped by the Greek goddess Hera to free her. Jason, Leo, and Piper go on a quest to free Hera who was imprisoned by Khione, the goddess of snow, in service to Gaea. At Camp Half-Blood, the Oracle of Delphi, Rachel Dare, gives them the Prophecy of Seven which foretells seven Greek and Roman demigods going on a quest to save the world.