Here is the official synopsis from Crepusculomeyer.com
The story tells Bree Tanner’s life and the new born vampires turned by Victoria in order to kill Bella. Bree makes friends, with sort of love interest with Diego, another vampire of the group, since both of them feel that have been used and have doubts about the real intentions of his leader, plus: her vision is different and bloodless than other newborn vampires. Diego mysteriously disappears,
leaving Bree even more confused and disconcert.
Through the road, Bree makes friends with Riley, a relegated vampire because of his power of release a terrible smell which upset others newborns He will convince her to participate into the battle, leading her to a terrible end in hands of Volturi who we will get to know through Eclipse history.