"Message from the Empress"
You get this in the third mission as you leave Daud's office to free one of your assassins. Turn around and look back at Daud's office and you'll see a large statue on the left.
Blink to the top of the statue. I had Blink level 2, and had no issue getting across.
Save the game unless you mess it up. Took me three attempts.
Now, look down over the statue's nose, and you'll see guys walking around. Wait for one to be *right under* you, now walk off the edge and as soon as you get close to the victim, press RT to do a drop assassination.