Shadows of Green by Tessa Carr

He’s her biggest problem.
Mellie Anne can’t seem to get rid of FBI Agent Max Lemons. He wants to protect her. She just wants to be left alone.
While visiting her late husband’s grave, Mellie is the target of an attack.
Max demands she follow his orders or face the consequences. When they’re thrown together in spite of their vexation with each other, Mellie realizes that maybe Max isn’t the enemy after all.