Finally finished the book. It was a short one I can tell you that!
It was one straight narrative with no chapter separation but it was vintage Stephenie Meyer---very addictive and hard to put down. You'll feel as much empathy for Bree as you felt for Bella.
The story covered the events that happened a week before the Victoria hatched attack on the Cullens at the end of "Eclipse". The story was told in the perspective of Bree Tanner, one of the vampires created by Victoria, to form her "vampire army". Bree relates the tumultuous relationship of the newborn vampires, the politics, and her shortlived second life friendships. The book also provided the unspoken communication by Bree and Edward during Jane's interrogation.
This book may also be the precursor to a series of Twilight offshoots with the introduction Fred, Shelly, and Steve who were to break away from the Victoria created coven.