Keys to the Crown by Leah Mara

After her mother’s assassination, Kiera gave up her crown to become a spy. She’s spent years training to earn the title of High Enforcer—the elite embodiment of justice in Rellmira. But first, she must prove she’s worthy by hunting down any threat to her father’s rule.
When a mysterious prisoner becomes such a threat, Kiera goes undercover to learn his true intentions.
But Aiden won’t reveal his secrets easily. His charming tongue spins lies as deftly as Kiera’s does, and he claims he’s just a thief looking for gold.
Upon their escape, Kiera proposes they work together on a risky heist—and Aiden agrees.
But the line between allies and enemies begins to blur as he slowly surrenders the trust she is now reluctant to destroy.

When the embers of rebellion, secrets, and desire ignite their world, Kiera must decide who she will be among the ashes—a traitor to her kingdom or to her heart.