Heir of Illusion by Madeline Taylor

An alliance between enemies. A weapon of untold power. And a bond that could rewrite fate.

Blessed with the power of illusion, Ivy Pomeroy has many tricks up her sleeve. However, none of them are a match for the enchanted collar at her throat that keeps her bound to a ruthless king. Forced to play the role of his obedient pet, she plots in secret to destroy him and claim the freedom she has always been denied.
When a mysterious reaper arrives in the city with his sights set on the same weapon Ivy needs, she must decide how far she’s willing to go for her freedom. With a tenuous alliance tying them together, Ivy learns there is more to her reluctant companion than meets the eye. He sparks her curiosity and ignites dangerous desires within her. But will their newfound connection lead them to triumph? Or will the secrets they harbor destroy each other?

Above all, Ivy must remember she is not the pet they tamed.
She is the beast they let inside.
And she will show no mercy.