The Assassin's Daughter - Akitada Mysteries, #15

Fifteen years after the brutal murder of an imperial prince, the crime casts its shadow on Akitada's family. The case is cold and the assassin dead, but his young wife's brother wants to marry the assassin's daughter, and Akitada is expected to clear his name. Worse, in doing so he must either destroy a friend's reputation or his own marriage. As Akitada searches for the truth among other suspects and unravels the secrets of the past, he stirs up fresh murder and shatters his own happiness.