The Wizard’s Mark by Janette Rallison

He was her first love. Now he’s her deadliest adversary.

By day, Marcella pretends to be a highborn lady, but at night, she’s a thief for the renegades, a group whose goal is to help servants escape their noble masters.
That isn’t her most dangerous secret. In a land where only men are wizards, she’s able to wield magic.
Marcella grew up as a serving girl in the castle where young wizards train. Falling in love with Ronan, the most promising apprentice, was a bad idea from the beginning. He’d made it clear he never planned on a future with her. It would’ve stood in the way of his ambitions.
Now the renegades want Marcella to go to the king’s court where an assassination might prevent a war, but then she’ll be back in Ronan’s path. This time as enemies.
He’s dangerous. He knows her secrets. Despite the sparks that always fly between them, he could easily destroy the mission and her.
And yet she might still be in love with him anyway.