Proceed through the door and kill the two sergeants and Imp over behind the cage on your left. Watch out for the two spectres and the two sergeants on the balcony.
Hit the western switch and head over to the now open door. Once they are all dead, move across in front of the door and kill the Imps 1. Hide where you can watch the red door and shoot the sergeants as they teleport in front on the door. Start off by grabbing the shotgun and then retreating back into the start room.
