"The Greek and Roman demigods must simultaneously prevent the earth mother, Gaea, from waking and stop war from breaking out at Camp Half-Blood"-- Provided by publisher.

"It's not easy being Apollo, especially when you've been turned into a human and banished from Olympus. On his path to restoring five ancient oracles and reclaiming his godly powers, Apollo (aka Lester Papadopoulos) has faced both triumphs and tragedies. Now his journey takes him to Camp Jupiter in the San Francisco Bay Area, where the Roman demigods are preparing for a desperate last stand against the evil Triumvirate of Roman emperors. Hazel, Reyna,...

Demigod Percy Jackson, still with no memory, and his new friends from Camp Jupiter, Hazel and Frank, go on a quest to free Death, but their bigger task is to unite the Greek and Roman camps so that the Prophecy of Seven can be fulfilled.

"Will the Greek god Apollo, cast down to Earth in the pathetic mortal form of a teenager named Lester Papadopoulos, finally regain his place on Mount Olympus? ... Now the former god and his demigod master Meg must follow a prophecy uncovered by Ella the harpy. Lester's final challenge will be at the Tower of Nero, back in New York. Will Meg have a last showdown with her father? Will this helpless form of Apollo have to face his arch-nemesis, Python?...

Uniting with Jason, Piper, and Leo after their dangerous quest, Percy, Hazel, and Frank wonder who will be chosen to fulfill the Prophecy of Seven, completing their group's number, and sail with them to an ancient land to find the mysterious Doors of Death.