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.

Jason, Piper, and Leo, three students from a school for "bad kids, " find themselves at Camp Half-Blood, where they learn that they are demigods and begin a quest to free Hera, who has been imprisoned by Mother Earth herself.

Athena and Hermes' search for the cause of their unexpected, life-threatening illnesses leads them to Cassandra, a former prophetess, who may be key to a war started by Hera and other Olympians who have become corrupt anti-gods determined to destroy their rivals.