Book 5 in the popular The Heroes of Olympus series.
Though the Greek and Roman crewmembers of the Argo II have made
progress in their many quests, they still seem no closer to
defeating the earth mother, Gaea. Her giants have risen-all of
them-and they're stronger than ever. They must be stopped before
the Feast of Spes, when Gaea plans to have two demigods
sacrificed in Athens. She needs their blood - the blood of
Olympus - in order to wake.