I just remembered this story, but I don't know where to find it. Maybe you can help?!
Here's the storyline:
Angel, Wesley, Spike and Xander are running Angel's Investigations in LA. Then Angel loses his soul. Angelus kidnaps and tortures Xander, then he turns him and leaves him for the others to find. They take him home and put him in a cell. At some point they catch Angelus too and lock him in another cell. Xander is very afraid of Angelus, because of the torture he suffered. I remember that Spike takes care of Xander and that they were involved even before Xander was turned, but nobody knew about it. At the end they manage to restore Angel's soul and put Xander's soul back in too. I think they shoot Angel with a gun, because they can't be sure if he really is souled again.
Thanks for your help in advance!