Shadow - Janie Crouch

Heath Kavanaugh lost years of his life working for a covert agency that ended up being the enemy. Knowing they put something inside his head—constant, incomprehensible whispers—is driving him crazy. 

He needs answers, but they’re nowhere to be found.

What he definitely doesn't need is to fall hard for his Linear teammate's younger sister, Jacquelyn—the adorable linguistics doctoral student who happens to be in the wrong place at the wrong time.

Especially when Heath’s attention puts her directly in the path of a danger he thought was gone for good. To stop it, they’ll have to figure out what’s in his head. And hope it doesn’t destroy them all.