A Spark Of Light by Jodi Picoult

At Mississippi's sole remaining women's reproductive services clinic, a gunman takes patients and staff hostage. The stories that brought these individuals to the clinic vary, from a woman awaiting cancer screening results to a protestor hoping to catch the clinic in a scandal that could be used in a pro-life campaign. Then there is the police hostage negotiator, whose daughter is also trapped inside the facility, and the gunman himself, who has a vendetta to carry out. Meanwhile, across the state, a seventeen-year-old lands in hospital after an attempt to self-terminate her pregnancy and is subsequently charged by the pro-life DA for the murder of her unborn child.
     As the book moves backward in time, each chapter set one hour earlier than the last, we learn how all these people and their stories are connected--and that none of these characters' reasons for being where they are at this fateful place and time are exactly what they appear at first glance.