The Truth About the Devlins by Lisa Scottolini

 The Devlins are a powerhouse  family in Philadelphia. Both parents and two of the kids are successful lawyers at the family firm. Then there's TJ, the hero of the story. TJ is a recovering alcoholic who went to prison for accidentally endangering a child, an act that haunts him to this day. The family regards him as a screwup even though he has worked hard to maintain his sobriety and to serve as an unofficial investigator for the family firm. 

One day, the family is celebrating the patriarch's birthday, when oldest son John, the golden boy, grabs TJ and desperately asks for help, saying he thinks he might have killed a man. TJ goes with him to the scene of the crime, only to find blood but no body. When they return to the family party, the father accuses TJ of drinking--and John totally throws his brother under the bus. TJ is determined to investigate what really happened to the accountant that John  supposedly killed, only to find cars following him around and electronic bugs in his apartment. It's a twisty story in which several of the subplots come together in the dynamic ending. 

Except for the fact that it took me a while to figure out that TJ was a man (Scottoline's progtagonists are usually women and I didn't feel she was totally successful portraying a male protagonist), it was a good story.