This Thing of Darkness — Barbara Fradkin

In the seventh book in the acclaimed Inspector Green series, an old man is found beaten to death on a street corner in Ottawa's Byward Market. Initially, the killing appears to be a mugging gone wrong. However, the mystery deepens when the victim is identified as Dr. Samuel Rosenthal, a retired psychiatrist with a contentious approach to life and treatment. Green discovers that the doctor recently changed his will to disinherit his estranged son and to benefit several former patients whom he believed he had failed. But who is the young mystery woman seen visiting Rosenthal's home every Saturday night? And more importantly, what does she know about the doctor's death? Green races to track down the young visitor, but he is unprepared for the final resolution, which leaves him grappling with the ultimate meaning of justice.