Trigger the Gala Event

 is a quest in the Fallout: New Vegas add-on Dead Money.

Quick walkthrough

 * Once you have placed your three companions (Dog/God, Christine, and Dean Domino) at their assigned quest-specific locations, you must activate the Gala event.
 * This requires you to activate the switch in the bell tower in the northernmost section of Salida del Sol. You will have to fight numerous Ghost People on the way to and inside the tower.
 * After triggering the Gala event, Ghost People will pour into the courtyard below the bell tower and you will have to fight or run your way back to the central fountain, near the entrance to the Sierra Madre Casino.

Detailed walkthrough

 * Father Elijah will tell you the only way to gain access to the casino is to 'Trigger the Gala Event'. This requires you to escort your three companions to three specific spots located around Sierra Madre during their respective quests: Fires in the Sky, Strike Up the Band, and Mixed Signals.
 * The quest will then start and will mark the Bell Tower where you must enter Salida del Sol and make your way through numerous Ghost People to get to the courtyard, from there you must follow a narrow route to the top of the tower.
 * There will be a console by a window facing the casino, once activated, it will reward you with a achievement: Having a Ball, 100xp, and the casino will come to life with fireworks, music, and lights. But it also gets the attention of the Ghost People, which flood into the area below.
 * Note that you can shoot the Ghost People with an automatic rifle or Holorifle from the windows of the tower, which should make things much easier on the way back. They will throw spears up at you, with remarkably good aim.
 * In the bell tower you can find the vending machine password for Super Stimpak and for the Holorifle focus optics mod.
 * You must fight (or run) back the way you came, to the central fountain in the Villa, before entering the Casino by the gate just behind it. You can simply run past the Ghost People if your health is low or you are low on ammo. They will not follow into the next section.
 * Finding your way out of Salida del Sol North after you trigger the Gala Event is made easier by the graffiti that this area's designers put onto the walls: numerous tags saying things like "Run, run, run!" are spread along the route out of this area. So, in general, if you see one of these tags in front of you, then you know that you are facing basically the right direction, and so should continue along that route.
 * Be careful of speakers! Upon activating the Gala event, some speakers will activate and it's difficult to exit Salida del Sol North the same way you came in. You can alternatively exit through the gate in the southwestern corner, just north of the entrance into Salida del Sol. You'll have to drop down from the rooftops into a courtyard filled with the Cloud, so before you do, locate the skeleton remains under an overhang close to the gate. That corner is safe from the Cloud and the key to the gate is on the ground by the skeleton. Grab the key, go through the gate, exit into the Villa.

Bugs

 * During the quest "Trigger the Gala Event", when you approach the control panel in the bell tower to activate the Gala Event, a scripting error may occur, which causes nothing to happen when activating the control panel which leaves the player unable to finish the quest leaving them stranded at the Sierra Madre.
 * After pulling the switch, glitchy floors may drop several of the enemies. The player may be dropped as well. When this happens, switching to third person will freeze the game.