Walk forward and continue down the hallway to the right. Follow this to the very end and turn left when able. Check out the right hand corridor for collectible (1/2). Kick in the door and continue through for a short cut-scene.
Head down the stairs and get into cover. You will get attacked by a big group of drones from the walkway on the second floor of the ruin here and from the ground floor. When they are dead, go through the arch and enter the courtyard area directly in front of you. As you enter the area within the ruin watch out for the theron guard perched in the spire at the back of the ruins. Take him out and some more drones will appear on the balcony. Kill any remaining locust on the balcony, and then head up the stairs and into the room beneath the spire. Hit the switch to open a door on the bottom floor. A pair of flamers and a couple of theron guards will come into the area.
Head back down the stairs and kill the locust here, head down the tunnel and through the now open door. Continue round to the left and exit into an open area; defeat all the enemies in the area and then use the lever just before the arch next to the building on the right of the room. Two doors to the structure here will open and let you through. Head down the spiral stairs here if you need some grenades, and then go out the door opposite the entrance.
You will enter a very large room, with a single piece of cover in the centre of the room in front of you. Behind this is a lever, pull it to have some cover appear for you. In front of you, at the far end of the room is a large group of drones. As they spot you, they will activate some mechanical cover, which will appear out of the floor in front of them and will attack you from here. Stay in cover and snipe them if you can. On a platform above this area to the right is another lever, occasionally a drone will appear here. Kill him before he pulls the lever or your cover will disappear and you will have to return to reactivate it. Whilst you are fighting with the drones, a reaver will fly in and attack you too.
Kill everything and move up to the drones cover, as you do the giant door behind it will open and two grinders will exit. Kill them and head through the door and follow the tunnel to the left. NOTE: If you want to earn the second collectible in this mission you will need to sprint down the tunnel to the left, follow it around to the right and up the steps, sprint into the closing door on the right before it closes to find collectible (2/2). Pull the lever here to exit.
Continue through the room, up the stairs and to the door. The next room is large and heavily populated with just about every type of locust you've seen so far. Fight your way through the room and up the stairs at the back. Exit through the door at the back and head up the stairs. And take the first left in the hallway.
The next room has a big semi-circular walkway leading under a makeshift bridge and up some stairs. In this room you will be fighting several maulers, some snipers, a couple of drones and some flamethrower goons. To make things easier, shoot the backpack of the flamer on the bridge to send him and his pals to their doom as the bridge collapses. Continue round the circular area and sit at the bottom of the stairs to pick off the maulers as they make their way towards you and then pick off anything else that's still alive. When you are done, follow the room layout up some more stairs and make an exit into a hallway.
Continue until you find yourself outside again. There will be some stalagmites around and a lever sitting in front of you between a couple of sets of stairs. Use the lever to activate some cover at the top of the stairs and walk up to them. In the centre of the room, some locust will spot you and activate a ring of cover in the central area. Eliminate the threat and take their place in the middle.
There will be a quick cut scene, and then you will have to protect Jack while he plants the beacon to summon reinforcements. In the meantime, you will have to chill out in the middle of the room here and defend your position from several waves of locust. Enemies will start running into the room from in front of you, for the moment it will just be drones and tickers. After you eliminate most of them a pair of reavers will fly over the walls around the room and start shooting you from overhead. Try and ignore them for now and defeat the remaining ground forces. As you do, two reavers will land and attack you.
Once the reavers have been defeated, part of the wall behind you will drop down and a few more ground forces will pour in to pay their respects. Make them extinct and you will complete the objective. Mosey on through the section of wall that has lowered and continue into the next area. You should now see some grind lifts falling into the area. When this happens, the big metal wall to your left will lower. Take cover as there is a group of drones just on the other side. Pull the lever behind the small section of wall here to activate some cover for yourself. One of these guys has a mortar, so try and take him out first.
Move into the next room when everything is done and dusted and another section of wall will lower. Take cover again and take these grubs out, once again one of these guys has a mortar so try to prioritize taking him out. After killing them all, you will see some more grind lifts coming into the area and at that time, the wall in front of you will lower. Quickly hit the lever nearby and take cover as two grinders and some tickers will enter the area. Behind these guys in the distance is another mortar guy at the very back. I suggest falling back to the previous set of cover and using a sniper rifle to smash the mortar guy's brain off from out of range if you can, then kill the tickers and finally the grinders.
Head up the stairs on the right and inside for a cut-scene. Follow the wall to the right round the corner and pull the lever on the far wall to finish the chapter.
