Mercer // Mercer's Vow — Heather Slade

He promised to protect her…Not to love her.Head of a private security firm, Mercer Bryant promised his partner, Kade Butler, that he'd secretly protect Quinn Sullivan at any cost. As a former CIA operative, Mercer knows his way around intense and stealthy operations. Trained in combat, he can get out of any situation -- and into any woman's bed. But when he starts to feel something more for the innocent and stunning Quinn, he can't stay away.Shipped off to a boarding school at a young age, the independent and feisty Quinn doesn't need a man to watch over her. But when she finds herself in danger, the only place she feels safe is the arms of the irresistible and rugged Marine. Hell bent on protecting her, Mercer takes on the vengeful Russians who are responsible for his partner's disappearance. With peril imminent and time running out, can Mercer save Quinn before the truth destroys their chance at a future together?While each book in the Butler Ranch Series is a standalone with its own HEA, they may be more enjoyable read in order.