The blood of Olympus - Rick Riordan

Though the Greek and Roman crew members 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.

The gods, still
suffering from multiple personality disorder, are useless. How can a handful of
young demigods hope to persevere against Gaea's army of powerful giants? As
dangerous as it is to head to Athens, they have no other option. They have
sacrificed too much already. And if Gaea wakes, it is game over . . .