Emma had her path set set in life, she was going to go to college and get a good job. Then things started to change, she didn't notice the black vans following her and her parents around daily. But when things reached a head and her parents died in a freak car crash that the local law were quick to dismiss, she started to question things. Then you show up, claiming to be her aunt/uncle and gave just enough info about her folks for her to trust you. You took her across the country to your home, hoping to keep her safe from the darker reality that now hunts her. (You get to chose what the big mystery is, maybe her parents were spies along with you. Maybe you're from the future and she actually is some relation to you. Maybe something supernatural is taking place.)