The Courier talks to Christine and asks her to go with them to the Puesta del Sol switching station.
Head west from the fountain, following the Pip-Boy marker, and go through Puesta del Sol to the Switching Station.
Once inside, approaching the locked interior door around the corner will cause Christine to direct the Courier to the fuse box on the wall near the entrance. This must be used to restore power to the station and open the door blocking the way. (The fuse box will also power up the nearby computer terminals in the same room).
The fuse box can be repaired with a Repair of 60 (there is a Fixin' Things on the large box to the left of the locked door), or use three of the electric box fuses found in locations in the Puesta del Sol area.
There is a fuse in the same room, in a toolbox near the computers to the right of the locked door.
Exit the station and go right, into the cloud. There is a fuse in a toolbox on the floor.
Also from the station exit, turn left instead and go down the wide stairs, turn left under the archway and keep going left until able to turn right. There will be a well-lit opening into a building. Enter and go to the top floor and out to a balcony, where there is a toolbox containing a fuse.
Once the door is unlocked, go through the station, dealing with the radio speakers found along the way. Check the walls for graffiti pointing out some of their locations. Christine's Signal Interference perk gives plenty of time to destroy them or run past.
There is one speaker to the right of the door as the Courier goes through, partially hidden behind the pipes. Another is high on the right-hand wall of the alcove they pass, to their right, in the same corridor. There is a third speaker around the corner and down the stairs, well hidden under the pipes high on the left-hand wall. All three can be destroyed with weapons, but not otherwise deactivated.
Enter the main station area and turn right, following the walkway. Christine will draw attention to the cloud below. The destination is across the broken walkway to the left. Below a large pipe is below which can be jumped on and run across to the other side of the room and then jump to the base of the staircase and go up, thereby avoiding most of the cloud.
To the right the walkway leads to a Dean's Electronics. It is protected by a shielded speaker, but Christine's Signal Interference perk will once again give enough time to run around the walkway and reach the terminal to deactivate the speaker. There is a tripwire just in front of the terminal; it can be quickly disarmed, or the speaker terminal can be carefully accessed and the trap then dealt with. Alternatively, one can disarm the grenade bouquet that would be tripped, carefully hidden on the left. The tripwire may already be disabled (or have gone off, possibly moving the Dean's Electronics book) when the building is entered.
Following the walkway left from the top of the staircase leads to a door into a room with a large computer on the left-hand wall, and a terminal in the opposite far corner containing messages related to the History's Sake challenge. Go through the door next to the first aid box on the wall and enter the next room.
Here Christine will draw attention to the ventilation control system terminal on the wall in front. Activating this will clear the poison cloud from lower levels of the switching station and from some areas outside in Puesta del Sol. Along one wall in this room is a fridge and a row of lockers, including Ennis's locker which contains the Remote maintenance terminal password. The lock can be picked with Lockpick 100, or opened with a key which is found in one of the rooms ahead.
With the cloud vented, it is possible to go back down the stairs and safely explore the previous room for a few spare Sierra Madre Chips and a skill magazine, some ammunition near the middle of the room, two stimpaks on top of the two big metal boxes next to the ammunition, and a toolbox. A corpse lies behind a fallen piece of walkway (below the entrance walkway), wearing a Dead Money jumpsuit and carrying the See you in hell asshole note. There are several bear traps under the large pipe crossed earlier.
Opening the door next to the ventilation control terminal reveals another walkway. There is a security turret to the right at the end of the walkway, and a shielded speaker on the wall to the left. The turret can be targeted and destroyed from inside the room the Courier is still in, safely out of range of the speaker, or deactivated at a nearby terminal, directions to which are noted below (although this requires avoiding detection by the turret while moving quickly enough to escape the speaker and jumping over gaps in the catwalk). Directly across is a locked door (Lockpick 75), behind which is the terminal to shut down the speaker. To reach the terminal without picking the lock, instead run down the stairs, take the first right then jump across the gap. Then go left up the stairs, jump the gap and go left again, looping around into the room behind the locked door (the door can be unlocked from this side via a wall terminal next to it).
With the speaker deactivated it is safe to return to the walkway. Again going from the ventilation control terminal, going down the stairs and taking the first right but then jumping the gap and going straight ahead towards the gray machinery will lead to a Special Ops Training Manual (follow the left-hand catwalk around the machinery).
Alternatively, turning right again before jumping the gap to the machinery, then going down the stairs and left over the pipe will lead to the aforementioned turret control system terminal, which requires a Science of 75 to access. Continuing along this path will lead to the destination at the elevator.
From the room with the speaker terminal, take the door to the right of the terminal and follow the walkway south to the main computer room. (It is also possible to reach the Chinese Army: Special Ops Training Manual mentioned above by jumping across to the right from this walkway.)
In the computer room there is a desk to the left with a terminal containing a note about Ennis's locker key. The key itself on the desk. Turning right at this terminal will lead to the destination in the next room.
Ahead is the maintenance elevator on the left. Across from it is the remote maintenance terminal. Christine will approach and initiate a conversation, expressing her fear and unwillingness to enter the elevator. With various dialogue options it is possible to deduce that she is remembering her experiences trapped in the medical clinic auto-doc, and is showing signs of claustrophobia (and possibly post-traumatic stress).
The choice made at this point will affect Christine's actions later in the game.
Lie to Christine and trick her into the elevator. This will complete the quest, but it will be impossible to use the elevator to quickly exit the station. Karma will also be lost for lying to her.
The Terrifying Presence perk can be used to scare her into the elevator, and still be able to use it to escape quickly.
Tell her another way to access the station controls will be sought.
The dialogue can be exited without deciding, and talking to Christine again will still give both the "good" and "bad" options.
The area can now be searched more thoroughly. Opposite the maintenance terminal and to the right of the elevator is the vending machine code for the Holorifle reinf. components, lying on top of a computer. Accessing the elevator and going down will give a written on-screen description of a tiny cramped room full of whirring machinery, exactly as Christine feared. Going up in the elevator leads to an exit back to Puesta del Sol - an upper floor room overlooking the street. Here there is a Fixin' Things on a desk to the left, Mentats on the floor an absinthe and Buffout behind a pipe above, and random items in the containers.
To help Christine, access must be gained to the remote maintenance terminal. It can be hacked with a Science of 100, or the Remote maintenance terminal password found in Ennis's locker can be used.
Talk to Christine again and tell her the terminal is usable. She will express her gratuitude and offer her hand in friendship. Once the dialogue ends she will take her seat at the terminal and the quest will be completed.
pc Sometimes, even when "Ventilation Control" is activated on the terminal that removes the cloud in the station, the cloud does not go away. [verified]
pc The objects within the switching station are very likely to cause the Courier to get stuck in scenery. No amount of running, jumping or any other trick gets them out once they are stuck, requiring going back to an earlier save.