The Son of Neptune is the second book in the Heroes of Olympus series written by Rick Riordan.
Wiki:
The Son of Neptune follows events after Juno/Hera "wakes up" Percy Jackson and he arrives at Camp Jupiter, the Roman equivalent of Camp Half-blood. Taking place around six months after the start of The Lost Hero, the Son of Neptune is told using alternate third person points-of-view of Percy, Frank and Hazel.
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