So I was doing this quest, and got to this part. I go to the basemant, talk to this Davison guy, and agree to help him get rid of the other guy. The other guy asks about the status of his friend, so I go down and check, come back up and give him the news, he leaves, and I get the intel Davison wanted. I go back to give it to him, and he attacks me. I kill him, and now I'm stuck at this stage of the quest. I killed all the Nightkin in the basemant I could find, looking everywhere, but none to be found. How do I fix this?

Actually, I figured it out. Some Nightkin was invisible and lurking in there. Only took me like an hour to find him. It's hard to find something that doesn't seem to want to come to you, is invisible, and is in a ridiculously dark corridor. I was able to track him by listening to his footsteps. Don't know if that's a bug or intended. I hope it's the former.

Intended, I think.
When hunting Nightkin, I look for the ripppling in the air, and the sound of their feet.

If they seem hard to find, turning on the pipboy light can help, just do not get mobbed.

...there's a light? ._.

LOL yea, there is. If you are on PC hold down TAB for a second or two (the same key that also brings up your pip boy).

Also, did you fail a speech check with Davidson or did you kill the jailer when you went to look for Harland's friend? There have been reports that Davidson turns hostile for various reasons and some say that they didn't change anything in their playthrough and he still turned hostile. However, you were able to finish the quest by wiping them all out, so that's good.

Edit: just saw that this is the xbox forum lol Sorry, don't know what button to push for the light on your controller, but try the one that brings up your pip boy.

All right, that would be the B button on my controller... I got the game on demand on Saturday, so I didn't get an instruction booklet DX

I went to Davidson and told him I'd help him get rid of the Ghoul, then went to the Ghoul and helped him to find out about his friend, and I had to kill the jailer on the way because all the Nightkin but Davidson were hostile. When I told the Ghoul about his friend, he left, I got the information Davidson wanted, and when I went back to him, he became hostile, so I killed him as well. That was where my troubles began.