The name Black Fang Brotherhood is most often whispered if mentioned at all. The Brotherhood is an organized band of cutthroats and assassins for hire.
Little is known about the inner workings of the cult, but it is believed that they worship a hideous demon servant of Death.
In Perelandra, membership in the Brotherhood is, while not outright illegal, certainly frowned upon. Any shrines or temples are kept hidden. Occaissionally the law enforcement officals shut down all Thieves' Guild activities in an attempt to get at Brotherhood members.