Cait will give you this quest once your affinity level with her reaches a specific level. She'll request for you to come with her in Vault 95 in order to find a way to permanently cure her of her extensive psycho addiction.
This area is occupied by Gunners, with assaultrons and a possible Legendary Gunner. You can find a cooking station on top of the vault entrance. From there, you have to take an elevator leading deeper into the vault.
After disembarking from the elevator, you can disarm the laser tripwires. The door to the immediate right is Advanced locked. Inside a terminal that you can use to deactivate the turrets. In the Overseer’s upper room, you’ll find the remains of some of the vault dwellers. The Overseer’s terminal there can be used to open the Master-locked Facilities Wing sliding door.
In the lower residential areas, find the room in the NE corner to find the Big Guns bobblehead sitting on top of the radio in the center table.
The residential room to the SW has an armor workbench and a Novice terminal in the next room.The lower floor of the main hall has another cooking station and a pathway leading to the vault’s reactor. If you follow it, it will go around to the eastern stairwell which will Lead to the lower main hall. Halfway in the eastern stairway, there’s an advanced sliding door. Inside, there’s an advanced floor safe and first aid box.
Continue to the Facilities Wing and follow the straightforward path until you reach the Detox Facility Terminal. From there, examine the detox seat and wait for Cait to get into the detox chair. Once done, operate the nearby terminal to start the procedure. Once done, talk to Cait and the quest will be complete.