Crossing the Line by A.L. Gomortis

Alex Thatcher is just settling in to her new life in Southern Arizona and her dream job as a Border Patrol agent. She is working with a respected mentor (and a newbie who is fun to boss around), learning her way around the desert, and even making some friends. But when Alex observes something unusual while out on patrol, she and her colleagues must work with law enforcement agencies and the medical examiner's office to investigate a series of homicides. Fascinating and suspenseful, 'Crossing the Line' captures the complexity and ambiguity of the borderlands.