Blood Ties — Ralph M. McInerny

Henry Dolan's granddaughter, Martha Lynch, adopted 23 years earlier, wants to find her birth parents. Her adopted parents are frantic over the idea of losing her, so Henry seeks out Father Dowling for help.
Meanwhile, Martha's birth father, Nathaniel Fleck, who left before Martha's birth, has contacted Martha's real mother, Madeline, for details about Martha. Madeline panics, afraid he won't leave her alone, and turns to Amos Cadbury, a lawyer, for advice. When Nathaniel is found murdered two days later, Dowling and Amos must juggle the responsibility of spoiling the peace of the families involved while uncovering the truth behind the murder.