It's where Bella is with the Volturi at some point and falls in love with a human who has a son. The Cullens end up back in the picture. The Volturi end up killing the human and his son which completely devastates Bella and I think she has a daughter, maybe? Eventually she ends up back with Edward and destroys all of the Volturi. I read it years ago but really want to read it again. Hopefully you know it!