As monsters walk the streets of San Francisco, unseen by humans, three teenaged descendants of Medusa, the once-beautiful gorgon maligned in Greek mythology, must reunite and embrace their fates.

With help from her new friend Orion, seventeen-year-old Helen Hamilton descends into the Underworld in search of a way to break the Furies' blood curse and prevent the start of another Trojan War.

Now united, the three descendants of Medusa must find the gate between the human and monster world to achieve their destiny.

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.

Greek and Roman demigods Nico, Jason, Reyna, Leo, and Piper try to stop Gaea, the Earth Mother, who needs the blood of two demigods sacrificed in Athens--the blood of Olympus--to awaken. Meanwhile, the friends keep having frightening visions of a great war at Camp Half-Blood that could be the end of all of them.

"Greek and Roman demigods from the Prophecy of Seven must work together to seal the Doors of Death--and help Percy and Annabeth escape the Underworld in the process"--