My sister called me one evening and asked if she could stay with me for a few weeks. She had just separated from her husband and said she needed somewhere quiet to figure things out. I didn't think twice about it. I cleared out the spare room, bought a few things she needed, and told her she could stay as long as necessary. For the first month, everything was fine. We cooked together, watched movies, and talked about what had happened in her marriage. I even helped her update her résumé because she said she wanted to start working again. Then I started noticing small things missing from the house. A watch I kept in my bedroom, some cash from a drawer, and a pair of wireless headphones. I assumed I'd misplaced them until my sister casually mentioned that she'd sold a few things to cover some expenses. I asked what things....