Sins of the Father by JA Jance

In Sins of the Father, retired Seattle cop (now PI) JP "Beau" Beaumont discovers he has a daughter he never knew about. It starts when a man named Alan shows up on his doorstep with a tiny baby and says he's looking for the baby's mother, Naomi, who had abandoned the baby at the hospital shortly after giving birth. When Alan shows JP a photo of the daughter, she bears a striking resemblance to JP's daughter Kelly. And when he hears who Naomi's mother is, he remembers a drunken one night stand from years earlier. So JP sets off to find Naomi and in the process uncovers several murders--and establish some kind of relationship with his daughter and new granddaughter. It's a good story, though there is way too much verbiage devoted to how bad the traffic is in Seattle!