Dishonored: Death of the Outsider

You'll get this on Mission 4 (The Stolen Archive). Make your way to the top floor of the Royal Conservatory and the Curator's Office. I came through the elevator shaft and snuck along the top of the main atrium/lobby but there are probably other paths you can take. You'll come across and Oracular Sister telling a maskless Overseer (Brother Cardoza) who is dissecting a dead witch that Sister Rosewyn wants to see him. An objective marker will appear and give you Rosewyn's location. Use Semblance to take Cardoza's face and then go talk to Rosewyn. She will hand you a silvergraph plate during a brief cutscene. When the cutscene ends both this and The Face of the Abbey will unlock.