The Evil Within À la Corvo Trophy / Achievement will give you one Bronze Trophy or 15 GamerScore Points. You need to get past your enemies without fighting them.
In this mission you should only kill the one zombie which you will see when you take the revolver. See to it that you don’t completely kill the zombies if you want to get this achievement. It is alright if they accidentally kill themselves by stepping into traps. If they kill themselves in this manner, it will cause no harm to your trophy.
As soon as possible, try to run and make your way out of the situation. You will need a crank to open the gate when you reach it. If, after reaching the gate, some of the zombies attack you, try to lure them away. Then you can return to the gate and open it.
Go through the video guide if you are still not sure: