Enter this room, kill the sub mutant with your axe and take the missile and the health.

Turn around and fire into the corridor. Switch to the axe. The two sub mutants will come at you, kill the nearest one and enter his room, turn around for the other. Then open the secret door and get the brass key.

If you at any time get very low on health make it to this room for some refreshments, take the water first. But beware the sub mutant and the ghost.

Continue.