Robert B Parker's Lullaby: A Spenser novel by Ace Atkins
The most unenjoyable part of this book is remembering how the title is actually listed in the catalog. Don't look up Robert B Parker as the author - look up Robert B. Parker as the title -- OK, my mini-rant is over.
The book is terrific vintage Parker. A 14 year old girl wants to hire him to solve her Mother's murder. The Police have a man convicted of the murder, but Maggie believes he is innocent and someone else did the killing. The usual jaunt through Boston and environs as only Parker can do. Yes, Hawk is in the story too.
A VERY satisfactory ending.