Angel found Fred, just as she was about to murder Knox. It seemed that the robots he developed for Wolfram and Hart had murdered her parents. Whether it was a tragic mistake, or deliberate, her parents were dead, and Fred was holding a gun on Knox.
Angel: Fred, you don't want to do this.
Fred: Trust me, I do.
Angel: You've never killed when it wasn't neccessary.
Fred: I tried to kill you.
Angel: Because you were convinced it was neccessary to stop evil. We can take him to the police, there's no need to take his life.
Fred: Do you really think you're in a position to lecture me right now?
Angel: I'm really more of a cautionary tale. And I need your help, and Wesley's help. You guys were right, that place corrupts you, and I need to get out. Will you help me?
Angel's plea affected Fred, perhaps they could be a team again. She shot Knox in the leg so he couldn't escape, then they called the police on him. Fred and Angel then went to see Wesley, perhaps they could help each other to stay good..