"A group of British graverobbers is active in this area, looking for cemeteries to ransack. Put a stop to their appalling activties."
If you have synchronized with this location then you can fast travel to the center of the search area making this much easier. Perform the Leap of Faith into the hiding spot. Duck over to the nearby corner and execute the nearby guard with a whistle and a corner assassination. Repeat this one the second guard that comes after him.
If you did not, you need to move in from the Southeast. Ever so carefully make your way to the center of the search area. There are numerous stalking zones and hiding spots you can use to make it there. Once you make it to the to the temple, make your way up.
The target is a Captain who sets off on a patrol when you enter the temple. This makes a direct approach the wisest. Sprint to the second door on the right. Set up for a corner assassination then wait. Your target will be along shortly.