The natural starting point for S.O.S. (if that name strikes your fancy) would be to expand Belethor's store to include facilities for the human trafficking operation, that he most obviously must be running on the side.
Additional content might include, among any number of other things:
- Adding Radiant Raiment as a merchandise supplier
- Adding dancers at some Inn (in the fashion of Desele's establishment in Morrowind)
- Having a link to the smuggler den at Brinewater Grotto
- Having a link to the Black-Briar family, possibly the otherwise phlegmatic son, or the daughters personal testing lab
- Having a link to the Silver-Blood family and their mining operation
- Having a link to the nice people at Fellglow Keep or Mistwatch
- Having a link to the Boethian cultists
One would need a fairly well developed quest, or two, or several, to tie it all together. Quests could be about unraveling the the nasty operation, or not. Possibilities here may be almost limitless.