Death of a Shadow - Barbara O'Grady Mystery Series, #4

The truth that could save two sisters lies buried deep. A desperate client storms into P. I. Barbara O'Grady's office, and begs for help finding her missing sister. Against her better judgment, Barbara agrees-the client reminds her of her own sister at her most needy.  Every lead takes Barbara deeper into the shadows of the past-and one step closer to the truth. But old secrets die hard.  And so will Barbara, unless she can beat a killer to his mark.