After you have completed the tutorial in the gardens, you will enter the mansion through a window. You will either take down, or avoid a guard. Steal his disguise, or one nearby. At this point, the game will allow you complete freedom of how to approach your target.
As there are multiple ways of completing missions in Hitman, I will simply provide notes about my approach;
- Avoided guard to my left by waiting for him to join the Head of Security (HoS) in the other room.
- Headed up the staircase to the left, and entered the bathroom (located across from the stairs and behind the guard at the balcony)
- Took Sleeping Pills and headed back downstairs
- Waited behind cover for the guard and chef to finish talking, and then walked through the kitchen, turned left and walked to the bar
- Carefully drugged the coffee on the bar, which will eventually be picked up by the HoS, who will then walk off to the right "to have a sit down".
- Followed the HoS after a few moments (you may need to hold RB to "blend" past the guards, though I did not have that option. Just quickly make your pay past them all) *Alternatively, backtrack to the kitchen, and walk through the door the guard used previously*
- Stole Keycard from HoS and hid the body in the nearby closet.
- Made my way back up the stairs, at which point the guard was gone. Walked around the right side of the balcony and unlocked the door.
-Made my way to the target and unlocked the achievement.
Obviously, there will be other ways of performing this assignment, but I've only just started playing the game.