The Lost Hero by Rick Riordan

From chapters.ca:
After saving Olympus from the evil Titan lord, Kronos, Percy and friends have rebuilt their beloved Camp Half- Blood, where the next generation of demigods must now prepare for a chilling prophecy of their own:
Seven half- bloods shall answer the call,
To storm or fire the world must fall.
An oath to keep with a final breath,
And foes bear arms to the Doors of Death.
Now, in a brand- new series from blockbuster best- selling author Rick Riordan, fans return to the world of Camp Half- Blood. Here, a new group of heroes will inherit a quest. But to survive the journey, they'll need the help of some familiar demigods.