"In the surreal, dream-like silence of Piazza degli Affari the sinister sound of the man's steps echoes beneath the porticoes. They are followed by quieter, more regular steps, muffled by the thick fog... they grow closer and closer, undisturbed and relentless."
For over thirteen years Margot Blanchard, young and charming chief of police in Milan’s Piazza San Sepolcro, has managed to hide any trace of her past, which threatens to undo the happiness she has worked so hard for, from her successful career in the police force, to her happy marriage and the birth of her daughter, Isabelle. But the past comes knocking on her door and, this time, there is no escape. The year of the World Expo, on Christmas Eve, a man is fatally stabbed in Piazza degli Affari. An impenetrable fog descends on the city, the streets are empty and there are no witnesses to the murder. The case is assigned to Margot and with the help of inspector Colasanti and agent Mantovani, she discovers that the victim is Mario Pittaluga, a financial consultant at the local branch of an established bank.
The inquest begins, but what appears to be the obvious motive for the murder is just a screen, hiding a more dramatic truth which will crush Margot with devastating fury and force her to confront the demons of a distant past from which she cannot run anymore.