Wait for You by Blye Donovan

When her little brother disappears, Imogen will do anything to find him . . . even infiltrate the household of an infamous lieutenant of the Lazcano Cartel.

Texas Ranger Mateo Travers has been working for the Lazcanos for over a year. He’s so deep undercover that he’s become the lieutenant’s right-hand man.
The end of his assignment is close enough to taste until the one woman capable of blowing it wide open shows up on his doorstep. Despite this snag in his plan, Mat can’t help wondering if fate is giving him a second chance.
Imogen Sanchez is on a mission to find her brother, and she won’t let the man who shattered her heart five years ago stop her.
Posing as a maid, she does the unthinkable—places herself in the path of the most feared man in North Texas. She knows the Lazcano Cartel had a hand in her brother’s disappearance. Now, she has to prove it.

Will she find her brother before the lieutenant discovers who she really is? Will her heart stay safe from Mat, or will he melt the ice guarding it?