While wandering through the ruins of Boston, the Sole Survivor happens across an area known as the Combat Zone. After dealing with the raiders whom took over the operation, the Sole Survivor is given Cait's contract by her manager Tommy Lonegan. Once she trusts the Sole Survivor, she will confide in them her past and her demons. Such as her psychoaddiction which is killing her - she asks to get her to Vault 95 where a rumored cure exists.
Upon discovering the raider stronghold within the Combat Zone, this quest will automatically begin, and the Sole Survivor will need to take down all of the raiders within.
After clearing out the raider population, there will be two sole survivors, standing in the arena, with a ghoul by the name of Tommy Lonegan beckoning for the Sole Survivor. Speaking with him reveals that he once owned the Combat Zone and catered towards the Commonwealth elite, until the raiders came in and took over the business, leaving him as nothing other than a lowly announcer.
At this point, Tommy will give the Sole Survivor a proposition, in that while he cleaning up the Combat Zone and getting it back to its glory days, the Sole Survivor will take Cait, the Irish fighter next to Tommy, with them out into the wastes.
Should the Sole Survivor accept and take Cait's contract, the two can then explore the wastes together, where, after earning her respect, she will begin to confide in the Sole Survivor more and more.
As Cait begins to warm up to the Sole Survivor, she will eventually confide in them over her chem dependency with psycho, and how it is beginning to kill her. She will mention that she had heard of a place called Vault 95 from before the Great War, that had revolutionary means in which to cure addicts of their addictions.
Upon arrival at Vault 95, it is discovered that it has been taken over entirely by the Gunners, who are using the area as a waystation of sorts.
The Gunners and their assaultrons will need to be taken care of, until finally reaching the vault's clean room, in which Cait will begin the detoxication process, and will finally have a second chance at being clean.
Bring Cait to Vault 95
Cait has confided in me that her dependence on Psycho is taking its toll on her health. I need to bring her to Vault 95 to cure her addiction before it's too late.
Locate the Clean Room
I've arrived at Vault 95 with Cait. I'm hoping the facility contains whatever it is we need to cure her addiction to Psycho.
Speak to Cait
Wait for Cait to get into the Clean Room Chair
Cure Cait's Addiction
Inside Vault 95 Cait and I have located the "Clean Room," an area dedicated to drug rehabilitation. After a short discussion, Cait has agreed to allow the Psycho to be purged from her body.
Speak to Cait
Cait's addiction to Psycho has been cured by a device contained within Vault 95.