In the House Party game, there are the last requirement challenge for Katherine in order for her to reward you. You need to locked the door of Madison’s Master Bedroom so that Larry’s cannot sneak a photo of her and no one can enter the room and disturb on what you both doing. The thing that you need to find for this last piece is a key called Mysterious Key, which is basically a key owned by Madison for her room. Madison probably place it inside the house. This key will allow you to locked the door of Master Bedroom and complete the reward of Katherine.
Master Bedroom Key Location (Mysterious Key)
You can find this Mysterious key on the living room where a women is dancing infront of a fireplace. The key is just on the shelves on the top of the fireplace besides the picture frames and base.
After getting that key, go to Madison’s Master Bedroom and there should be a new selection for “Lock”. You can now locked the door and talk to Katherine to get your reward. Don’t forget to press P in order to get your clothes.