This is a decision trophy near the end of chapter 7.
You will be on a balcony and be given two choices, go right to save Gould or go left and save the civilians.
For this trophy choose to go left and save the civilians. This is Adams' path.
After making your choice make sure to kill all the enemies silently or you'll be forced into a firefight.
The trophy will not pop until after you have killed all the enemies and triggered the end of the level, so you have to do a second playthrough for the opposite choice.