Henning Mankell: The Man Who Smiled [2009] paperback

After killing a man in the line of duty, Inspector Kurt Wallander finds himself spiralling into an alcohol-fuelled depression. He has just decided to leave the police when an old friend approaches him for help investigating his father's suspicious death. Kurt doesn't want to know. But then his friend is found shot dead. Against his better judgment, he returns to work to head what may now have become a double murder case. But while Wallander is on the trail of the killer, somebody is on the trail of Wallander, and closing in fast.