When searching for the second book the doctor needs in the royal bunker, you will come across a door requiring a code that is obtained in the warehouse you go through. However, you cannot get the code until completing the Tower of London mission and receive the ability to read the Enochian language. Return to the warehouse and clear the area around the keypad, then enter the office beside the keypad room. Look through the glass towards the keypad and notice that the Raven of Dee above the keypad door is incomplete. Also there are some incomplete paint marks on the glass. Move around so that they line up, then scan it to obtain the code. Note: There are four digits spread out in the bunker. Besides the one in the mirror by the door, you can find others by following the trails revealed by your blacklight.