The Assassin Dominic Monroe

After witnessing the brutal death of an informant, a young woman is swept into a deadly realm of espionage and adventure after she follows a stranger up the stairs one night at a party, and from that moment forth, her world as she knew it, would never be the same. The stranger is a spy. Forced to trust her with his secret, forced to trust him with her life, they find themselves on the run from the world's most deadly assassin. When betrayal implicates his former partner at MI6, an old flame reenters his life, further complicating his assignment and his growing affection towards the young woman. When the girl is kidnapped and an old friend is murdered, he disobeys a direct order and seeks revenge. On the verge of losing everything, his job, his career, even his life, he comes dangerously close to turning into an assassin. Determined to find her and kill the traitors, he is forced to make a decision, choose between her life for his enemy, or sacrifice his life to save hers. Because after you do it for a while, it becomes easy killing people, it's like breathing.