Answer: Where the Tower of London collects Yidi's letters: Didn't you pass by a boat when you first arrived at the Tower of London? That's where the sniper rifle was taken. There is a door that needs a card to get through. After the computer is upgraded, the door can be opened. The letter is on the boat, with a shotgun beside it. "Zombie U" Novice Raiders Black Screen Solution Modifier Using Extra Weapons Envelope Location Archive Location Test Experience Achievement Trophy Configuration Requirements