The Old Men of Omi. Akitada Mysteries, #13

A. D. 1030.  Senior Secretary Sugawara Akitada is recovering from a knife wound and still reeling from the loss of his wife. When the Council of State orders an investigation of the claims of two warring temples, he is sent to Otsu to clear up the matter. As it happens, Akitada's best friend Kosehira is governor there and welcomes Akitada into his large and cheerful family in hopes of healing his mind and body.
But almost immediately, the murder of a judge interferes with both the official assignment and the planned relaxation. When other murders follow and the local authorities express endless faith in his skills, Akitada gets on the trail of a serial killer. Meanwhile, the violence simmering among the monks escalates. When Tora is attacked and held by them, Akitada must use his diplomacy to release him, but the incident sends Tora and Saburo on a desperate and dangerous mission in the mountains. To make matters worse, the lonely Akitada has fallen in love with his friend's nineteen-year-old daughter, an impossible situation that nearly drives him to distraction.