Selenomancy, Percy Jackson

In which a golden-eyed traitor begins to question where her loyalties should lie.
In which Percy Jackson somehow can't keep his eyes off a certain daughter of darkness.

In a world of gods and monsters, Luna Corvo, a powerful and cunning demigod, walks a dangerous path. Aligned with the notorious Luke Castellan, she is captured and brought to Camp Half-Blood. With her mission compromised, Luna must now navigate the complexities of her divided loyalties.
And the closer she gets to Percy Jackson, the more she realises that the fate of Olympus may very well rest in her own hands.

(Book one in the moonlight series)
(The Titan's curse - The Last Olympian)