I don't have a title. Can you guys help me?

Do you ever feel like your older sister could lead a double life as a secret agent? I've always felt that way. My sister, Joan, is always sneaking around the house. Silently. It's creepy how she does it. She also finds things she shouldn't (but we're both really good at that), like where I hide my money and where my mom puts the M&M's. She's also really good at lieing. I think I'm better, though I don't lie a lot. I try to be good. Both of us are black belts in Tai Kwan Do, but she is just scary sometimes. You probably think it's just sibling rivalry and paranoia. I used to believe that too-until I was in her room looking for some socks and found a paper with the letters FBI on it by accident.