Try to get the Super Officer in this next corridor around the corner with your plasma gun. He will leave you a missile launcher. Take the cross. Don't take a death chalice. Take what health you need.

Go down to floor 1 here (green arrow).

Find yourself on floor 1 here (red arrow). Open the door and go past the death chalice.

Try to hit as many of these enemies with your two missiles then switch to plasma gun. The guard in the next room to the south and the sub mutants in the rooms to the west will be alarmed. Pick up the different types of ammo left by the fallen enemies. Beware the two bombs by these doors.

Find an extra missile in this little room.

Reinforce in the kitchen...

...and in the dining room. But watch those two guards hiding by the fireplace.

Continue.