The Man Who Smiled (original: Mannen som log) is a novel by Swedish crime-writer Henning Mankell, and is the fourth in the Inspector Wallander series, although the English translations have not been published in chronological order.
After killing a man in the line of duty (in The White Lioness), Inspector Kurt Wallander finds himself spiralling into an alcohol-fuelled depression. He has just decided to leave the police when an old friend, Sten Torstensson, approaches him to secretly investigate the recent death of his father in a car accident. At first Kurt dismisses his friend's suspicions as unlikely, when Sten is found dead, murdered with no doubt, in exactly the same manner as a Norwegian businessman shortly before. Against his previous judgement, Kurt returns to work to investigate what he is convinced is a case of double murder.