When you first start the game you have to go through and obstacle course and battle 2 bad guys. When Giles opens the door for you, you need to go thourgh and open the first to doors. After the 2nd door is a room with hay. Climb up the hay barrels to your left and look to your right. There should be a chair there. Kick it and it will break showing a glowing object. Pick the object up with your Y button, and you have an extra stake then to your right(not down from the loft) is a table with another glowing object on it. That is your mission key that will open all doors. Then just continue to the end!