Purchase the Rat Cave from the town hall. After it is finished being built, wait until you get a call that a criminal is in town. Do not put on the rat suit, and find the criminal. When you find the criminal make sure there is a person in the room who needs to calm down, cheer up, etc. Go to that person and calm them down, cheer them up, etc. If the criminal gets near you while you are doing this, you will pass out and go to your room. It will then be dark everywhere. To reverse this, simply calm someone down, cheer them up, etc.