At top of stairs is a room with a few Locust in it. Go out on the balcony and kill the last seeder. When it is dead, go back in the room. The Locust will rip open the door to the left. Take
Cover behind whatever is nearest. Kill the Locust as they try and breach the room.
Go out the door that the Locust just opened. Head to the right as you enter the new hallway. Follow this hallway until you get to a room. Kim will talk to Alpha Squad again. Continue down the hallway until it turns right. Now head down this hallway until Marcus enters the room.
Kill the 2 Locust in this room and head out the door on left side of room. Go down this hallway until you reach a rock in the wall. At that point some Locust will come out to play.
Kill the Locust and continue to follow the hallway. At the end of the hallway will be a hallway to the left. Enter this hallway and then duck into the one to the right.
Follow this hallway. When Marcus reaches the couch a few Locust come out. Kill these Locust. Continue to follow the hallway until you reach an opening to the left. Go down the stairs.
Go out the door and turn left to shoot the Troika gun emplacement.
After the Locust manning the gun emplacement is dead use the emplacement to kill the Locust coming down the hallway.
Go to the right from the gun emplacement. At the T section head to the left. Follow this hallway until you get to the left turn. Follow this hallway around to the stairs. In the big room at the bottom of the stairs are several Locust. Kill the Locust. Go to the left. Climb the stairs.
At top of stairs is a big room with a table in the center. Go around the table and up the stairs.
At the top of stairs is a Troika gun emplacement facing away from you. Kill the Locust controlling it. After the Locust is dead man the gun emplacement yourself. Kill all the Locust on the ground and in the air. When they're dead a cut scene begins.