Following the Clues in Highland Park

M10 - Following the Clues in Highland Park is a mission in Deus Ex: Human Revolution.

Infiltrate the mercenary compound
Jensen finds himself in a parking lot filled with guards. The goal is to enter the nearby warehouse and take the elevator inside the warehouse down into FEMA's compound. Beyond simply fighting your way though, there are several ways to enter the warehouse. Inside the warehouse itself are four more guards on patrol, a sniper in a catwalk, and a guard in a security shack. The elevator itself is down a ramp. A vent system connects the first floor and the catwalk. Call and enter the elevator to finish this part of the mission.
 * Directly across the parking lot from the door through which you entered this area is a fenced-off section with a hackable lock. Hack the lock, enter, then take the ladder located there to a door in the roof.
 * Almost directly beneath the roof door is a door on the ground floor. There is a guard stationed immediately before this entryway.
 * On the far side of the warehouses are some boxes. Jump over these to reach the back.

Locate the mercenary leader
The elevator takes Jensen down through a series of floors, each of which has guards engaged in various preparations. These guards cannot see you in the elevator. However, when the elevator ends, be ready to move. You find yourself in a large room. On the ground floor is a 80-X Boxguard and two soldiers. Above them is a series of catwalks with a further three soldiers. To sneak across this room you can: Once through, you are in a passageway in which two guards are talking. Eventually one of them will leave while the other will begin a patrol. You can take him out. There is also a ladder that leads to an upper corridor that will take you right past this guard. Both ways lead to a large FEMA holding center. However, both ways also offer different options. The holding center itself has two levels. The upper level consists of a series of catwalks patrolled by three guards and monitored by one camera. You can sneak past these guards or, with careful timing, take them out. The ground floor consists of a series of holding cells, a turret, cameras, and several patrolling guards. Upon first entering the lower level, there is a vent hidden behind a box immediately to your left that makes it easy to sneak past the guards. Alternatively, using the ground floor security office to change the turret to ENEMIES makes the whole room much easier.
 * Go right. To the right is an entry to a stairwell that leads up to the catwalks. You must evade two cameras on the way up. Once there, either take out the guards or sneak past them.
 * Go left. There is a large holding area in this direction, access to which is blocked by a wall of large tubes. However, stacking the nearby crates allows you to jump over these tubes and use the cover of the holding area to move past.
 * Go up the middle. It is possible to hide beneath the platform immediately to your right upon exiting the elevator. This way is perhaps the most difficult.
 * Staying on the ground floor takes you past a security office. The security hub in this office gives you access to some of the cameras in the holding center as well as a turret.
 * The upper corridor leads to a room with a second security hub. Hacking this security hub gives you access to an armory in this room.

It is possible to explore the holding cells. There is a small amount of loot. There are also several Pocket Secretaries with messages from the people who attacked Sarif Industries. As only one guard patrols the corridors between the cells, and there are only a few cameras, it is easy to explore them without taking out everyone in the room.

Once through the holding center, you find locker rooms, a cafeteria, two medical bays, and a small armory. Depending on the route you took, you may come across two FEMA employees. The employees will not automatically attack you. If you let Zeke Sanders escape from the Sarif Factory at Milwaukee Junction, then met him in Detroit as part of Voices from the Dark, you will have a password that allows you to get past these employees and a passcode to all relevant doors. If you did not have access to Sanders for whatever reason, then you can still intimidate the employees to make them let you through, but they will attack you if you attempt to hack any doors in their presence. Talking to the two FEMA employees and intimidating them does not cause you to lose the Ghost bonus. Whichever method you take, it is worth exploring the locker rooms, armory, and medical bays for supplies. Additionally, a small room behind a level three lock contains a special eBook. If you want to hack this door, and the aforementioned employees are still alive, then stack two of the nearby cardboard boxes in front of the window to obscure their view.

Once through this area, take the elevator down to a large empty warehouse. The warehouse is initially dark. Then sirens sound and lights come on. There are no enemies here, so proceed as you like. Go to the end of the warehouse, follow the corridor behind an office, and come to a set of closed doors. Triggering these doors initiates the fight with Barrett.

Boss Battle One: Lawrence Barrett
Kill Barrett by any means. Barrett's primary armament is a machine gun that can overheat. His secondary armament is throwing a cluster of grenades. If he gets in melee range, most of the time he will kill Jensen outright. Ammunition is scattered around, and there is also a locker full of shotguns. A cheap way to kill him is to throw the barrels at him until he dies. Pick the barrels up, stay behind the concrete pillars and throw them at him. While he is stunned, shoot him with the rocket launcher. If you continue to run around the outside of the room and continue to throw barrels and alternate with the rocket launcher, you will kill him. Possibly the quickest way to kill him is to shoot him once with a rocket launcher and then use the typhoon augmentation.

Meet Malik at the original landing site
Take the quick exit door ahead.

Barrett Tactics

 * Barrett attacks primarily with his minigun-arm and also throws frag grenades. He will melee the player if he gets too close. This melee attack can be used to the player's advandage. If the player is able to absorb the damage dealt by the melee (50 health points), the player will be saved from any grenade explosions, so he is effectively invulnerable. This tactic is however very risky.


 * Supplies are located throughout the edges of the room, and there are several pillars and boxes for cover.


 * The best place to hide is behind the box in the supply room - Barrett will not enter there even if you are spotted. He can, however, clusterbomb the area with multiple grenades, making it a dangerous spot to be in if you do not have the rebreather, EMP protection, or are trapped between him and frag grenades.


 * Various items in the room (boxes, fire extinguishers, gas canisters, and especially explosive barrels) can be thrown at Barrett, and many will stun him. This is a good method for sneaky players who are not outfitted with heavy weapons. In fact, explosive barrels are so effective, as it takes just a couple of barrels plus several shots to take him down, even on the highest difficulty. Be careful when attempting so because Barrett can shoot and blow up the canister in Jensen's face, killing (explosive barrel) or seriously injuring him (gas canister).


 * Barrett is vulnerable to headshots, as well as EMP, concussion, gas, and frag grenades. At the easiest level, Tell Me a Story, he can be killed with 3 frag grenades.


 * Setting traps using UR-DED or proximity mines works well.


 * Barrett can be stun-locked with the P.E.P.S. or the stun gun. Given enough ammunition, he can be killed with only these weapons (15-20 darts on Give me a Challenge).


 * If the player hides long enough, Barrett will eventually kill himself with his own grenades.


 * Using the rocket launcher can end this fight quickly. Two hits with the rocket launcher and a few shots from the pistol or machine gun are sufficient.


 * Using the Typhoon Explosive System is effective but risky. At close range, Barrett will melee, instantly killing Jensen most of the time.


 * The game can be saved during the encounter.
 * A very simple tactic is to hide behind the concrete barrier in front of you as you enter the room. Barrett will unload his minigun at you, chipping away at the barrier, but you will remain safe. His gun will eventually jam, at this point you can pop up from cover and unload several rounds to his head. Once his gun is cleared he will start blasting you, so it's time to hide again. Repeat this three or four times for an easy and safe kill, where you never have to move.
 * Director´s cut tactic only, for stealth players: in two corners of room (the closer one is on left side of your starting position in the room) are now two ladders leading up to floor above, which is not visible on the map until you enter the room with Barret. Use your cloaking ability to get up there. On this floor are a shotgun, some painkillers, ammo and a computer, which you find once you go through the ventilation shaft.  If you hack it, then you can open a garage door with some inactive turrets. Return to the ladder you climbed, turn on cloak and enter another shaft at the end of a newly opened alley behind the corner. Enter the office through shaft, hack the computer and turn the turrets to shoot down enemies. As Barret is a boss, this should not compromise your Pacifist achievement. Alternatively, one could lure Barret into one of the rooms opened via said computer, lock the doors behind him and trick him into blowing himself up with his grenades. Note: It is possible to tank the damage if you have overchared health.
 * Directors cut only. Run to the ladder on the left mentioned in the previous bullet point. Go up and into the same vent. Halfway through the ducting is a grill where you can see the floor below. It's possible to shoot Barret through this grill with something like a rocket launcher or a sniper rifle. Barret will know you're there, which keeps him in eye line of the grill. He will try to throw frag granades at you but these will explode harmlessly. Just keep taking pot shots until he's dead.
 * If you have two EMP grenades and the Shotgun, simply hide behind the first cover and throw an EMP. Run to Barrett and unload as much shotgun shells as you can before he regains his senses. Repeat and he should die. A good way to finish him off if he managed to survive is to cloak and run circles around him, as you shouldn't need a lot of shots and the cloaking will make him slow to target you.