In this page you can find a detailed description of "Ghost Warrior" achievement that you can unlock in Get Even. You get this trophy for reaching the meeting place on swamps without raising an alarm.
Warning - If you were detected and you alarmed enemies you don't have to replay the entire level. You can simply select the option to load the last checkpoint and replay only the most recent part of the memory.
You can get this trophy during "Jasper's Dying Minutes" memory that is reserved for Black. When the level starts you begin near a small tunnel that leads to swamps. There you can find three areas in total that are occupied by enemies.
In the first part of the swamps you must watch out for the nearest enemy that patrols the area near a container. Move through the right side of the map, this will allow you to go past all other enemies. The exception to that is the enemy presented in the picture above, the one that stands near water. Fortunately, you can easily eliminate him with a headshot (zoom in with your phone to aim easier).
In the second part of the swamps you must also stick to the right side of the map and when you are standing on top of rocks you must look around for mercenaries that can be killed.
The exit from this part of the swamps is presented in the picture and before you use it you should wait until one of the guards goes left. You can also get to that passage while you are crouching. By doing that you can be sure that no one will notice you (and even if someone can see you then they will be in "yellow status" which means that you still have your chance to get this achievement).
Going through the third part can be the most troublesome because the last ruins are full of enemies and the sitting one, presented in the picture above, is the most problematic out of them all. Don't try to kill him because this alarms his buddy causing his status to become red which means that you won't be able to get the trophy. Instead of that you can act in one of the two different ways - be at the edge of the sitting enemy's field of view and lure him out so he separates from the rest before you attack him or you can go through the ruins behind him. In the second option you alarm another guard whose status becomes yellow. When this happens you must withdraw quickly or avoid him and eliminate when he goes into a secluded place.
After solving the problem with the guard that was described above you must focus on going through the right part of the map. If you stay in a crouching position you shouldn't raise any alarms.
The trophy is unlocked right after you leave the swamps and get closer to the big building (at the same moment you will hear Red's commentary).