Your first task in the mission called "The Deserter" is to find and interrogate a group's leader. The meeting is held in a such place that prevents you from stealthy eliminations. When the leader sees a gunshot, he gets into the car and starts running away. The only thing that you can do is to get into a vehicle and chase him.
During the chase the only thing that you must do is to stay close to the target. At some point the leader has a crash with another enemy vehicle. When this happens, leave the vehicle and interrogate him. A new place is marked on your map, you must get there.
You are now in a place where there is much more enemies. The right flank is the best way to finish the mission. From there, you have a good view on enemies that are grouped in a such way that you can finish them by using synchronized shot. Remember to not kill the deserter marked in yellow.
When you have the possibility, approach the deserter and catch him. Meanwhile, your allies should take care of the remaining foes. When they deal with everyone, get to the back doors of a car, place the deserter and get behind the steering wheel.
Get to the appointed place and, during that, avoid the enemy patrols.