Faithless by Karin Slaughter

The victim was buried alive in the Georgia woods–then killed in a horrifying fashion. When Sara Linton and Jeffrey Tolliver stumble upon the body, both become consumed with finding out who killed the pretty young woman. For them, a harrowing journey begins, one that will test their own turbulent relationship and draw dozens of life into the case.

For as Jeffrey and Sara move further down a trail of shocking surprises and hidden passions, neither is prepared for the most stunning discovery of all: the identity of a killer who is more evil and dangerous than anyone could have guessed.