My step-sister was coming over for dinner as our parents were out of town. She said she’d be arriving earlier than me and she’d let herself in and wait. I got home from college and saw her car. I let myself in the house and called out to her but didn’t get a response. I could hear a faint noise coming from upstairs. I went upstairs and had a look around. Out of the corner of my eye, I could see that my bedroom door was aj...