The Orphan the Marine and the Mastiff

Mei Mei was orphaned at the age of six. She has been alone for so long that she can't remember a time when she didn't feel lonely afraid and forgotten. Then one day, just as she was settling in with another temporary foster family, a case worker came and took her away again. Somehow Mei Mei had a brother. A grown-up Brother, and she was going to live with him. Mei Mei didn't know who or what this brother person was supposed to be, but she was sure he wasn't supposed to be the stern scarred giant that she meets in the caseworker's office. Resigned to her fate, she has no choice but to go with this brother, but she doesn't have to like him, does she?
Brother was born to a young teen mom. Fortunately, he was adopted and raised by good people. Brother joins the Marines and served with heroism and distinction for several years and many deployments all over the world. An IED ends his career and leaves him depressed, scarred, and broken. During a long and troubled recovery, he is surprised to learn that he is the only relation to an orphaned younger sister who is alone in the foster care system. The choice is clear, if he doesn't adopt her, likely no one will. Can he make the change from a decorated war fighter to single parent?
As these two stranger siblings try to build their own family of choice, they will find themselves surprised by mystery enemies, brilliant friends, unexpected adventures, and the love of an apricot English Mastiff.