Michael Collins: The Slasher (USA 1981)

From the Publisher:
SLASHER CLAIMS TENTH VICTIM!
Dan Fortune gets a call from his old flame, Marty Dekker. Married for the second time, living in Malibu, she needs his help. Her new husband's niece has become the victim of the feared Canyon Slasher.

At least, the murder fits the psychopath's M.O. But Marty doesn't believe the Slasher killed Suzanne Dekker. Can it be, Dan wonders as he heads for L.A., that Marty has doubts about her handsome novelist husband, about his real relations with his niece? And is she counting on Dan's loyalty no matter what?

Michael Collins: The Slasher. A Dan Fortune Detective Mystery. Playboy Paperbacks, ISBN: 0872168557 (July, 1981), 204 p., $2.25.