Allison pulled up to her parents' house, the snow crunching under her feet as she walked up to the door. She had offered to watch her seventeen year old sister Mary, while their parents went on a cruise to the Bahamas.Allison had offered to watch her sister, as their parents didn't want Mary left alone for two weeks, since they had given Allison a cruise of her own for her twenty-first birthday. Allison knocked on the doo...