Heroes of Olympus: The Missing Eighth.
Summary
Andy has thought he was a normal demigod. Until he was swept away to a deserted island, with none of his powers. Percy Jackson and the other 6 come to find out the Oracle made a mistake with the prophecy. She mean't to say:
Eight 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
They suppose that the Protector of Water, Andy, should be the eighth person of the Prophecy. They must find him before Gaea rises.
Characters
Andy Gerion
19- Son of Poseidon and Protector of Water