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.
Returning from camp, eleven-year-old Tash is dismayed to find that her elderly next-door neighbor has disappeared and is compelled to use the key that may possess magic.