"Steal the printing plates" is a mission objective in Sequence 7 / Memory: Unbreaking The Bank
Walkthrough[edit]
The printing plates that you are looking for are found on the Northern face of the building. They are somewhat close to the open window on the third floor of that face of it.
There is a Watcher by this window. Use Eagle Vision to mark them and wait for the nearby Brute to move away. Once the Brute does, enter through the window, eliminate the Watcher (and the Brute if they were closer than you thought).
Once inside, you can head into the Southern room on the third floor to Burn the counterfeit money. Otherwise, head down the stairs in the middle of the building to the second floor.
At the bottom of the stairs, look around the corner to the North. You will see a Watcher who is nearby the plates that you are after. Move in quietly and eliminate them.
Evie pays a visit to the center of London after Jacob's assassination of Twopenny.