True Evil by Greg Iles

FBI agent Alex Morse is stunned to discover that her sister, Grace, has had a stroke. She arrives just in time for Grace to tell her that her husband planned her death. Alex feels she must investigate in order to protect her nephew, Jamie, from his father, whom she considers a murderer, or at least an accomplice. Her investigation reveals an intricate and devious plan to get rid of spouses of wealthy people, leaving no trace of what killed them. This leads her to Chris Shepard, a doctor in Natchez, Mississippi, whom she believes will be the killer's next victim. Alex and Chris work together to try to unravel the mystery of who is behind the murders and to keep Chris out of harm's way. Iles has written a suspense novel full of interesting characters, lots of action, and a good sense of place. A page turner.