From the start of the video immediately get frisked by the guard walk through the hallway into the staff only area and up the stairs. As you climb the straights and go through the door take a right, and then climb up the wall DON'T go up the ladder run to the left of the wall continue straight and then climb the ladder on your right.
Sneak up to the guard and subdue him drag him into a hiding spot and then take his clothes and GUN. This will allow us to walk around ALMOST freely only the ICA agents will make your disguise LUCKY when we see one just run past them it inst enough time for them to clock your agent 47.
Now run past the two guards on the roof and take a right and go down the stairs all the way to level -2. Be careful as at the bottom of Level -2 you will bump into 2 guards who will make your outfit. They will go right at the bottom of the stairs WAIT in a hiding spot as they will then double back and go left.
Once the go left run down the last bit of stairs turn right and then goes through the double doors on the right this takes you into the Club owners office. sneak to the left hand side of the office you will see a Gramophone on the table go turn it on and then go back behind the wall next to the desk. The club owner will go turn it off go behind subdue him taking his clothes.
Finally we need to hide the body and PICK up the phone book the owner drops. On the table next to the bar you will see a phone this will let you arrange a meeting with the ICA do this and then go over to the chair and sit down.
Once the call is made you will hear that the ICA know your agent 47 don't panic stay seated and wait for all the 5 targets to walk into the room. When the ICA agents are in a position flip the table and pull out your gun shooting dead all the targets.
I found it easier to use the pistol however on the bottom of the desk is a shotgun, Its all down to personal preference. Once you kill the 5 targets some more guards will rush into the room kill these and the exit will be just to your right hand side out the office.