Fallen Star by Michelle Madow

In the treacherous world of the fae, promises are binding, and love is the most dangerous game of all.

Sapphire Hayes thought her biggest challenge would be escaping her small town in Maine.

Then she fell into the fae realm, discovered her hidden magic, faced execution by a mad king, and survived three deadly trials set by the infuriatingly handsome prince Riven.
But surviving the trials was just the beginning. Now, Sapphire’s on the run with Riven and her best friend Zoey—as fugitives from the Winter Court. And while Riven might be slowly stealing her heart, Sapphire’s guarding a secret that could change everything.
Because she’s not just fae. She’s also part vampire. And her bloodlust is growing stronger by the day, turning her into a monster that Riven will surely want to destroy.
As if things couldn’t get worse, a dark-winged creature snatches Zoey away to the mysterious Night Court, leaving Sapphire with an impossible choice: help Riven find an ancient potion that could restore peace to his kingdom, or rescue her best friend from the enigmatic Prince Aerix—a captor whose seductive cruelty might be the deadliest game of all.