A Darkness More Than Night by Michael Connelly

When a sheriff's detective shows up on former FBI man Terry McCaleb's Catalina Island doorstep and requests his help in analyzing photographs of a crime scene, McCaleb at first demurs. He's newly married (to Graciela, who herself dragged him from retirement into a case in Blood Work), has a new baby daughter, and is finally strong again after a heart transplant. But once a bloodhound, always a bloodhound.

Delia Hopkins has led a charmed life. Raised in rural New Hampshire by her widowed father, Andrew, she now has a young daughter, a handsome fiancé, and her own search-and-rescue bloodhound, which she uses to find missing persons. But as she plans her wedding, she is plagued by flashbacks of a life she can’t recall.