The Fall of Amethyst

After learning that she's the reincarnation of the Greek deity, Amphitrite, Amy has dealt with a lot. From the mental whiplash of her childhood friend Percy actually being Poseidon to the unforgiving push into an ancient war against Zeus, she's handled it. But just when Amy's beginning to accept that the world is more vast and magical than she thought, she's betrayed by someone she trusts. Now she finds herself being held prisoner by an enemy much more sinister than Zeus ...
Amy is determined to keep her faith in Percy coming to rescue her, but her captors are equally determined to turn her against him. And there's only so long she can withstand mental and physical torture, no matter how intriguing she might find one of her captors.
As Amy's resolve grows weaker, and the call of the trident grows stronger, she is faced with the fact that not only is she in danger, but she might also be the danger.