Desolate Escape by Sherri Wilson Johnson

It was just a weekend reunion among old friends. How did it turn so deadly?
Dr. Lacey Elrod is the first-ever medical examiner for her hometown, a place that should be safe from serial killers. But when someone murders one of her high school best friends on the morning of the wedding of two other friends, Lacey must trust U.S. Fish and Wildlife Officer Matthew Flick, the man she left fourteen years ago, to keep her safe and help her find the Dunes Killer before he strikes again. After more murders among their friend group, Lacey and Matt suspect one of their old friends of being the Dunes Killer. But when that friend turns up dead too, they must work together to rid their town of the killer.
Can Matt move past his hurt with Lacey for how she handled their unwanted teenaged pregnancy and how it ruined his plans to go into the ministry? Will Lacey be able to forgive herself? Both struggle with their faith and with each other as they track the Dunes Killer before he succeeds at killing them.