This discussion may contain spoilers!
When leaving the apartment, Beauty was being unusually secretive, asking Bigby not to tell her husband that se had left, but why? And in the following chapetr's preview, we see her in the strip club. What reason would Beauty have to go there?
In Fairest, it was revealed that the Beauty we know is not the reak Beauty, but Lamia, another Fable that killed her and stole her life. She currently believes she is and behaves like the real Beauty because she has began to believe her own lies, but every couple of decades her real personality emerges back, and she becomes a serial killer, targeting rapists, wife batterers and other men who mistreat women. And she WAS seen in a strip club in that preview, so this seems like the perfect setup for Lamia to come back.
Add to that the fact that Bigby knows about Lamia, and that he has threatened Beast with solving the Lamia situation himself if Beast can't handle it, and suddenly their fight in the preview makes a lot more sense.
Granted, there are a couple problems with this theory, not the least of which being that when Lamia comes back, Beauty disappears. And of course she can't be responsible for Faith's and Snow's murders, she only targets men. But, seeing as we're dealing with a serial-killer who seemingly targets only young women, I believe this is a chance too juicy to pass up.