The Knock

It was three in the morning. I was alone in my rented apartment when I suddenly heard three knocks on my door. "Knock, knock, knock." I looked through the peephole, but the hallway was empty. Just as I was about to go back to my room, my phone rang. It was a message from my friend who lived next door: "Are you home? Whatever you do, don't open the door. I just saw on the security camera that a woman has been standing outside your door." A chill ran down my spine, and I immediately replied, "But there's no one outside." A few seconds later, my friend replied: "She wasn't outside... she was standing right behind you." I spun around. The room was empty. Just then, a soft female voice came from the closet behind me: "You finally found me."