Stalker.

You've had a stalker for about a year now. He sends you letters constantly. At first, it was only once a week. But now they've started coming every day. He's broken into your house several times, but you have no evidence, so you can't call the police. And you're afraid to. And now you're at home, sitting in your chair, reading a book. You've never seen him, all you have are letters and the feeling of his presence, which frightens and unsettles you.