This mission will see you fighting all by yourself, separated from your squad, at least for the majority of its duration. Walker will begin by falling down from the flagpole, pursued by a large wave of sand. As he hits the ground, he will roll and stumble into a position behind a car on the deserted street. There are enemies nearby, and they'll hone in on your position fast. You will have to survive until Adams and Lugo arrive, and you'll start out with only a desert eagle to make matters worse. Enemies will come in from the left, right, and above, but mercifully not all at the same time. Find the nearest enemy, who should be approaching from the left, and take him out with the desert eagle. Pick up the M4A1 that he drops and take cover behind the car.
From your position behind the car, use a combination of your pistol and the various weapons that the enemies drop to take down the oncoming waves of bad guys. Stay alert as more and more enemies enter the area. Watch out to your right for a shotgunner who will drop down into the battlefield shortly after the chaos begins in earnest. Take him out and loot his shotgun before turning around to the left and eliminating the wave of advancing enemies from this side. Grab their UMPs in stead of your M4A1, which will probably be running short on ammo at this point, and return to your original position behind the car. Keep an eye out for enemies trying to flank. At this point, you will be getting hit from the left and the right pretty hard, and a few sly enemies will no doubt try to take advantage of the confusion by sneaking up on you. If you have any grenades left, now would be a great time to toss them out into the fray, just to cause a distraction if nothing else.
Lugo and Adams should be getting close by now. You will just have to hold out for a few more seconds before help arrives and the rest of the enemies are driven from the area. After a terse greeting, the three of you will set off down the city's abandoned street, towards more trouble. Head down the corridor between the rows of abandoned cars, looting corpses for ammo as necessary. When you approach a white SUV and a piece of metal sticking up in the air from the sand, the refugees will kick over the metal debris to form a makeshift bridge ahead, from the other side of which they will begin to attack you. Take cover behind the white SUV to the right of your location and return fire, downing the enemy. Leave your cover and head across the bridge. Grab a few extra sticky grenades from the chest just opposite the bridge, and then head down to the left past the shipment truck.
You will meet up with more enemies here. One will be hiding behind a shipping container, while another will be by a large truck in the distance. Still others will be hiding to the right of the large white truck, waiting for you behind cover. Run up to the shipping container on the left and take cover behind it, only peeking out to shoot any enemies who show their faces. When the area seems cleared, head around to the right and take cover on the shipping container here. Four more enemies will charge you from the end of the alley. Use blind fire to take them out, as they will be in a small concentrated area and can be easily killed here. Follow your squad to the end of the area when they're all dead, and man the turret while Adams attempts to open the door ahead. You will ahve to protect him while the gets through the door. Enemies will come from several locations during this assault. They will begin in the shipping crate below and among the cars to the right. After these initial waves are over and done with, more enemies will come out from atop the toppled metal supports over and to the left of the billboard ahead. Keep an eye on the top level to take out the rest of the enemies before following Adams and Lugo into the next area.
The next area, as it turns out, will be full of corpses. You will be walking through what amounts to a graveyard. Even in this grim scene, don't neglect to grab Intel. You will find a piece of Intel located to the right of the hallway, just before the rows of dead soldiers in chairs. Proceed to the end of the hall for a cutscene, in which you and your squad will find the CIA operative being used as bait. After the cutscene, it will seem as if a battle is inevitable. The 33rd had set up a trap, and you and your squad sprung it nicely. You are surrounded and it seems as if there will be no way out. At the last second, help will come from a most unexpected source. As C4 drops in from the ceiling, one Sergeant Riggs will cover your escape with grenades from an elevated postion on the ceiling. It's now or never, and you'll have to get yourself and you squad out of the death trap and to safety while Riggs covers you. Take cover behind the column and shoot a clear path ahead before sprinting ahead and taking cover behind an overturned table next to the wall. Eliminate the remaining enemies from this position.
Sprint forward and loot the chest for grenades by the next piece of shoulder high cover. More enemies will begin to shoot at you from the other side of the balcony. Carefully proceed towards your waypoint marker. In this section, you don't necessarily have to kill all of the enemies in the area to advance. As you approach the first waypoint, be wary of a shotgunner who will be hiding behind the central column in the double doors. Take him out and then proceed forward, being sure to watch out for the two enemies who will run out into the hall to avenge the shotgunner. Keep moving down the hallway and you will soon make it into the next room. More enemies will be cowering behind tables and couches to the left of the entryway in this room. Take cover by the overturned table to the left and return fire. Order your squad to suppress the enemies in their positions while you flank around to the right and attack from behind the stand with the broken skeleton on it. Watch out for more enemies hiding behind the intact dinosaur fossils. Shoot them through the legs of the dinosaur and keep moving towards the waypoint, which will have shifted to the other side of the room.
When you reach the area with the large T-Rex skeleton, you will have to kill three more enemies on the other side of the room. After doing this, a cutscene will show a helicopter flying down to your level and laying down fire on you and your squad. The giant skeleton will come toppling down in front of you, along with much of the other contents of the room. You cannot kill the helicopter in this section; you must simply run away from it and hope for survival. Sprint towards the opposite side of the room, staying low under the gunfire, and curve around to the right at the end of the hallway. This will lead you to a circular staircase. Follow it up the stairs and then run straight down the path, curving slightly to the left when the path ends. This will trigger another cutscene in which Adams takes a bullet to the leg before the three of you ultimately escape from the helicopter, although only by a slight marigin as it bombs the museum. This will mark the end of the level entitled "The Pit," and will send you and your squad battling on into the next level.