Ruthless Heart by Beth Williamson

He led her astray, and she never wanted to go back.

Sheltered all her life, Eliza Hunter never imagined herself alone in the vast Utah plains, much less trailing a mysterious, rugged man hired to hunt down her beautiful younger sister. Unable to reveal the truth about her pursuit of him, Eliza plays student to the teacher, transforming herself in the process. And she when she finds herself sharing the warmth of Grady’s campfire, wrapped in his arms, hypnotized by his power, soon she is a naive spinster no more…

Grady Wolfe is more than a loner, he’s a man forever on the run, an assassin with a dark past and an even darker future. With a body and soul finely honed from living off the land, Grady knows he should leave the irresistible woman alone, but she stirs something in him he hasn’t felt before. Now he’s lost in the woods for the first time in his life—with a dangerous job to do. And no one—not even the distracting Eliza—is going to stop him.