It was the phrase 'the only thing Papa filmed that year' - the fact that a man on death's doorstep would make the effort to film a patch of wall - that really sparked Montalbano's curiosity . . .

When Inspector Montalbano's town of Vigàta is selected as the filming location for a new movie set in the 1950s, the director asks locals to dig out old photographs from that time.

And that is how engineer Ernesto Sabatello stumbles upon a mystery. In his attic, he discovers a series of films shot by his father between 1958 and 1963, always on the same day - 27 March - and always of the same subject: the outside wall of a country house. Intrigued, Montalbano begins to investigate the meaning behind these peculiar films.

Meanwhile, a local school is attacked by a group of armed men. As shock ripples through the community and the police attempt to track down the perpetrators, Montalbano must consider taking a closer look at the students themselves and delving into the world of social media.

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