Night Watch 
 This is one of the most difficult missions in the game.  It is also one of the best, because it requires to use stealth tactics for the whole mission.  I have decided to skip ahead and do this walkthough early, because I have gotten many, many emails asking for help on it.  Keep in mind that when I made this walkthrough, I was on 00Agent, so some of the phones and evidence won't be there if you are playing on only Agent or Secret Agent.
The very first phone tap is simple.  Turn around, and it's on a cabinet right behind you.  This one is only here on Secret and 00Agent, though.
Jump out the window, and go straight to this gate.  Shoot off the lock, and take out the guard that's in there.  Remember, you can't kill him, so stun him and punch him out.
You will need to take out another guard that is patrolling around the guard house, then go inside, take out that guard, and use the Data Scrambler on the little computer thing.
Then backtrack to the gate, and go left.  Stay right next to the wall, and crouch, so the guards don't see you.  If they do see you, it's not the end of the world, just disable them all.  Not impossible, but difficult indeed.
In the next area there will be a guard by the pool, take him out quickly, because the next part takes some time.
Carefully go to the next area, disabling the guards you need to.  Stay to the right, and creep up to the door, and enter the Villa.
On the left wall of this room, there is a cabinet with another phone on it.  Stick a phone tap on it.  Turn around, and go deeper inside the villa.
There is a guard inside here, so be careful.  Look for a smaller hallway off of the main one, that looks like this.  There is another phone on the small table there.
Exit the house, to this area.  There are a couple guys in here, so do what you have to to get rid of them.
Go straight, until you get to another guard hut.  you know what to do, take out the guard, Data Scrambler on the computer.
Turn around, and continue to this point here.  Go into the wooden door in font of you.
There are no guards in this room.  Go straight, and take a right into the small room.
There will be two guards in it.  But there is also a safe, which you need to use the Safe Cracker on.  Then, use the Camera to take a picture of the papers in the safe.
Before continuing, exit this building the way you came, and go to the fence.  Shoot off the lock with either your Silenced P2K, or your Watch Laser.  Using the Mustang will alert the guards.
In this fenced in area, there is another guard hut, disable the guard, Data Scrambler, yadda yadda.  Then go back into the last building, and continue through.
You will see a long patch, with an arch in the beginning of it.  There will be several guards here on 00Agent, so be careful.  There are no guards on Agent, however.
You will come to this spot.  This is nearing the end of the level.  But you still have one more phone and two more pieces of evidence to find.  There are all in that hut, and there is nobody in it to stop you.
Shoot out the window first.  This will save you some time.  You can get that phone from outside.  If you look across the room, you can also photograph the second to last piece of evidence.
For the last thing, run into the hut, and you will see Davidov coming.  Don't worry, you have plenty of time.  Take a picture of that clipboard on the desk, then get out of there.
Go to the back door of the car, hit B, and the mission is completed.