Michael Shayne's Long Chance — Brett Halliday

A search for a missing girl takes grief-stricken Mike Shayne to New Orleans

It was a knife that brought Mike and Phyllis Shayne together -- the murder weapon that Mike had to prove Phyllis did not bury in her mother's back. But years after they met, fell in love, and got married, Phyllis is dead, and the knife is just another blade. Grieving the loss of his wife, Mike decides he has had enough of Miami, where he and his beloved made a life together, and plans to move to New York and start again. But the South is not through with him yet.
 
As Mike prepares to leave Miami for good, a worried father comes to him, begging him to help find his missing daughter. She is a depressive morphine addict who recently tried to take her own life. When that failed, she fled to New Orleans to throw herself into the arms of the drug. In order to help protect the girl from herself, Shayne musters up the strength to go to the Crescent City, but terrible dangers await him in French Quarter.

Michael Shayne's Long Chance is the 9th book in the Mike Shayne Mysteries, but you may enjoy reading the series in any order.