The Combat Zone (quest)

The Combat Zone is a miscellaneous quest in Fallout 4.

Detailed walkthrough
The entirety of this quest takes place within Combat Zone as soon as the doors are opened, which some raiders will be defending in a small camp on the outside.

You enter into a foyer with two bound raider "rulebreakers" taunting you from the cashier's cage. There is an advanced terminal which unlocks the cage door, but you can't free the raiders or anything. There is an expert safe and some loot in the cage. Upon entering the main room, you will come upon the end of a cage fight in progress with Cait and an unnamed raider, with several raiders watching on as Tommy Lonegan provides commentary. As you walk further in, the raiders will instantly become hostile and attack the Sole Survivor. There are 4 raiders, 3 raider scum, 2 raider psycho, and 1 raider waster.

After clearing the area, you will find Cait and Tommy hiding inside of the cage on stage for their protection, and after approaching Tommy he will be both grateful and enraged that his only form of clientele have been butchered before his eyes, and comments that he wonders if he should thank you or have his "little bird" disembowel you in front of him. After a brief talk, he realizes that Cait is a liability (and an addict), and insists that the Sole Survivor take her from him until he can straighten things out and eke out a better life for them both. He also awards you the purse of the last fight, and you are free to loot the rest of the building. From there, speaking to Cait will allow you to use her as a permanent companion.