From the main menu simply navigate to the "Campaigns" section then go into the "Hitman 3" scroll across to "On top of the world" Select and play.
As soon as the mission starts run up the stairs in front of you and take a left. As soon as you turn left you will see a small crowd next to a bar head over to the bar and wait for the event staff member to come out inspect the food and return into the back room(For me he was already going into the back room).
Follow the event staff member into the room wait for the door to close behind you and subdue him, once he is subdued take his clothes. Run to the left and enter the double doors that lead into the kitchen walk down the stairs into the changing room on the bench you will see some "Transfer documents" pick them up make sure your NOT seen.
Now you have the documents turn right go through the double doors and then exit the kitchen turning right. Once you have turned right you will see a door that is open you will need to run into that door but be quick a guard in the hallway will make your disguise if he sees you for too long.
Once you have entered the room pull out your camera and scan the window once scanned it will open you need to wait for the event staff member to leave and subdue the guard taking his clothes. turn around and leave the door you came in from.
On your right you will need to run up the stairs and go all the way to the top run towards the penthouse reception and take a left going through the double doors. AS you leave to your left you will see the security room enter walk towards the guard sitting down and announce that you have arrived.
The guard will then call Marcus Stuyvesant wait for him to arrive. Once he has arrived he will ask for your transfer documents you picked up previously hand them over and then he will ask you to follow him. Do just that follow Marcus
Eventually he will lead you under the helipad you will see 4 targets swinging in the wind. Marcus's Bodyguard will place 6 knifes on the table pick them up and throw them at the targets knocking all off them down. Once you have done this Marcus will walk over to the edge of the ledge DO NOT push him yet. After admiring your skills Marcus will dismiss his bodyguard before returning to the edge of the ledge once again.
All you have to do now is wait for the Bodyguard to get out of sight before kicking Marcus over the side of the ledge. This will then pop the achievement.