This achievement is gained over the span of 2 levels.
This is pretty close to the beginning of the game.
First, you must not be seen in Act 3 by a specific guard (see below).
Then, you must Pull the fire alarm before ending the mission in Act 4.
Technically, there are multiple ways to complete each level.... however, this is what I found to be the fastest, and most foolproof PATH.VOLUME 1, ACT 3: Casing The Joint
Pick the lock of the truck.
Take the cleaning uniform.
Go left, pick the lock of the fence.
Go around the house (left), enter the kitchen, keep going right into the house.
Cutscene begins, showing you BOGDAN.
Run to the right side of the house, outside.
Along the way, press
on Bogdan to Examine him.
Find the mop and Press
to BLEND IN.
Wait until Bogdan has a phone call and eavesdrop.
Once done, run to the left side of the house outside, to find another mop.
to BLEND IN again.
Bogdan will come over here and have another phone call - eavesdrop again.
Try to go upstairs, a guard will go HEY! Now just walk away.
The guard will go upstairs, follow him (not too closely).
Elite1111111111 added: You can wait until the actual party to get the security code. That way you don't have to risk going upstairs when you shouldn't be up there.
At the top go LEFT and pick the lock.
BUT HURRY!!THE BEARDED GUARD THAT GETS OFF THE ELEVATOR - HE MUST NOT SEE YOU.
Go sneak behind the desk and Hack the computer.
Make sure you are crouching/sneaking the WHOLE TIME in this room.
You will make a phone call (cutscene). Keep sneaking!!!
The guard will come in and then leave. NOW you leave.
Go back downstairs. Exit through the kitchen.
Exit through the front yard.VOLUME 1, ACT 4: Party And Larceny
Walk up to the crowd of people, a guy MIRON will talk to the guard and then walk away - follow him.
Talk to him.
Tell him all 3 things that are YOU GETTING INTO the party. Pretty obvious choices.
Follow him upstairs & inside - MIRON will tell you he sees his girlfriend - and he runs upstairs.
Don't follow him. Go talk to his girlfriend and tell her MIRON is upstairs.
Go find BOGDAN and pickpocket for his keys. I found him upstairs to the right, in the "smoking room."
Use the elevator to go downstairs to the garage.
Head to the right (avoiding the guards) - to find the room - Pick the lock
- BUT NO BIKE! UH OH!
Sneak back upstairs (via elevator) and the cutscene shows the bike on right side of the house.There is a FIRE ALARM you must pull, it's to the left of the stairs on the 1st floor.
PULL THE ALARM.
It will beep and Bogdan will talk about it.
Now walk up to the Bike (yes Bogdan is still on it...) - and press
This will end the level - and the Achievement should pop immediately