Achievement Tip // That's a Knife
Perform an Assassination on an Enemy
Since the Jackals here will be distracted by other soldier, you should be able to sneak up behind one and perform an Assassination. Approach an unsuspecting Jackal (or Elite, Brute, Grunt or human) from behind and HOLD the RIGHT BUMPER down to execute a melee attack. If you are positioned correctly, you'll perform an Assassination with your knife in a cool animation.
Enter the door on the north side of the plaza and you'll find a large supply of M392 DMR Designated Marksman Rifles -- pick up a DMR and heal with the Medkit on the ground if you need to.
Several waves of enemies will now appear thanks to a Dropship to the south. Focus on sniping the Jackals (Skirmishers) off the rooftops first, then take shots at the Grunts and Jackals with shields before dealing with the Elites.
If you need to grab a Plasma Pistol, do so -- the Grunts should drop one in the plaza. Use it to overload an Elite's shields, then finish it off with your DMR.
After a second wave of the same enemies, Kat will finish fixing the door. At this point you can just retreat inside the northern door (the dark area with the DMRs and Medkits) and wait until it closes.
Turn on night vision by pressing LEFT on the D-Pad. Follow the hallways back and a cutscene will occur once you stumble across a dead body.
After the cutscene you'll find yourself facing down several Grunts, and an Elite. Between you and the enemies are several cargo crates which you can use for cover. Grab a DMR off the wall by the door before proceeding.
Since you are in tight quarters, now is a good time to use grenades on clumps of enemies. Hopefully you can weaken the Elite in the blast. They'll retreat up a ramp and several shielded Jackals will block the way. Send a grenade their way and finish them off. Finish off the Grunts in the hallway and move down the ramp into the next area.
Take shots at the Grunts below in the next room. Once they are all eliminated, look for a Plasma Pistol -- you're gonna need it! Two Elites guard the panel you need to reach in a small room on the other side of the storage area. One of the Elites has an Energy Sword, so keep your distance. One hit with the sword and you're dead.
Pick an Elite and hit it with a charged Plasma Pistol shot. Immediately follow this with DMR fire and you should be able to take it out. The Elite with the sword may try and charge you. Use the same technique but back away and fire if it gets close. You should be able to take it out before it gets to you provided its shields
Activate the panel marked on the wall in the small room to end the mission.