Mission 3: The Good DoctorAfter making your way into the Addermire Institute, you'll find the main staircase toward the back of the building. Climb up to the fourth floor and watch out for the two guards between the second and third floors. At the top of the stairs, two more guards will talk before splitting up. Take out the guard that stays inside then follow the other guard to the right and out onto the terrace.
Once outside, the guard will patrol to the left, you should go to the right. Make your way to the far end of the terrace and climb up to the roof. You'll see a taller rooftop ahead and a series of smokestacks. Climb onto the smokestack closest to the taller rooftop then Blink/Far Reach up. This is where you'll make the drop. Look below for the patrolling guard that we passed earlier. When he walks under you, jump down and hold
to knock him out or
to kill him. Either way, the achievement will unlock!