When you head through the next door, you will stumble upon the civilians who had been living in the camps. Unfortunately, they will have been rounded up by the 33rd and are currently being escorted out of the area. You and your squad will have to do something, and fast. Follow the circular stairs as they lead you down towards ground level. You will soon be met by an enemy on the stairs. Gun him down and take cover on the inside wall of the stairs. Continue to loop down the spiral staircase towards the lower level, shooting more enemies as you go. There will be another one on the stairs, as well as a few off of the stairs armed with grenade launchers. Take out the grenade launcher enemies first, and then leave the stairs to the right.
Run over to the balcony to get a good view of the floor below you. It will be crowded with several enemies, so shoot them from above or toss a grenade down to kill them before proceeding to the lower floor. You will have to contend with more enemies here. They will shoot at you from the opposite side of the balcony. Take cover by the desk and use Lugo's sniping abilities to take out the farthest enemies while you concentrate on the closer ones. As you advance down this hall, more enemies will come out from the other side of the hall to face you. Gun them down. Watch out for possible Stun commands here, which you can use to have your allies toss out stun grenades.
Run to the opposite end of the hall and search the corpses for a grenade launcher. Pick it up, swapping out whichever of your weapons currently has less ammo, and take cover on the edge of the ledge to the left of the stairs. Peek over your cover and hit any enemies you can get in your sights with grenades from your grenade launcher before swapping back out for a more reliable weapon and proceeding down the stairs. Watch out for a shotgunner coming down the hall to the left. Take him out and then proceed down the walkway to the right of the area. Take cover against the column here and peek around to see more enemies swarming on the other side.
This floor and the floor below you will both be swarming with enemies as the rock music reaches a crescendo. Focus on the enemies who are currently on the same level as you and leave the ones below you for later. Pick off enemies from your position by the column, and order Lugo to snipe any enemies that prove to be troublesome. When the floor that you are on has been cleared, take cover on the other side of the walkway and look over it to examine the battlefield below. There will be several red explosive crates scattered about the area below you. Wait until a sufficient number of enemies are near the crates and either shoot them or, for an extra bang, toss a grenade down next to them. The explosions should take out a good amount of the enemies waiting for you below, making it less dangerous to run down and mop up the rest yourself.
As you make your way to the left side of the level, you will come across several areas where the walls have been blown out. Use this to your advantage by peeking through the gaps in the walls and shooting the enemies below. When you reach the stairs, turn around and run back to find a chest of grenades before running downstairs. Take cover on the low wall at the bottom of the stairs. A turret will pin you in your cover. Toss out a stun grenade right next to the turret and, when the turret is stunned, pop out of cover and shoot the explosive crate to take out the gunner. This will trigger four enemies, including a shotgunner, to run out from behind the turret. Shoot them as they make their way across the labyrinthine path below, and use squad orders to keep them suppressed.
At the bottom of the stairs you can find another crate of grenades, along with a crate of stun grenades to the right. Grab them both and run out by the sandbags. Collect weapons and ammo from the fallen soldiers and then take cover behind the sandbags as more enemies come in from the left of the area. Jump over the sandbags and take cover behind the couch. You will find an ammo refill box. From this position, use grenades and stun grenades to keep the opposition pinned until they bring out a turret. You will now have to run around and stop the turret yourself, as your squad is pinned and providing a distraction.
Run around to the right and vault over the table. Look through the gap in the wall to the left to find an enemy. SHooot him and continue onwards. Run down the narrow corridor. A person will run out screaming in front of you. Don't shoot, as this is a civilian. Note that it doesn't really matter if you do end up shooting her by accident, but hey, it's always nice to spare the innocent and besides, these are the people you're here to save, so just let her run past. Continue on through the corridor, and a real enemy will soon pop out. Shoot him in the head and keep running, looping around to the right when necessary. You will stumble upon the turret soon. Toss a grenade out into the little clearing ahead, as three enemies will be here and they won't take kindly to your intrusion. You will catch them by surprise, though, so you should have just enough time to toss out a grenade before retreating a little to let it detonate.
With the gunner dead, take control of the turret yourself. Enemies will be on the balcony to the right. Bury them in sand by shooting out the giant windows behind them with your turret, and then pick off any remaining survivors. More enemies will attack you from below, so turn the turret on them and wipe them out before they can become a nuisance. As the sand falls in through the walls, all of the remaining enemies will be buried. Walk off of your position and climb onto the mountain of sand. Lugo and Adams will meet up with you here, and they will inform you that the 33rd managed to escape with some of the civilians. You did manage to save some of them, at least, and with that the three of you will walk back off into the desert to prepare for the next mission.