The title is from the Bible and implies that humans have a less that perfect perception of reality.
I can't think of a better title for this Guido Brunetti novel, which grapples with unambiguously moral and ethical issues mostly having to do with the environment of Venice. Leon's mysteries have always been set in Venice, and often touch on the sticky problems surrounding the polluting of the lagoon, the crumbling of the edifices and the navigation of Italian bureaucracy. But, this is Leon's first foray into the pollution issue as a major theme.
As usual, we have Inspector Vianello and Signorina Elettra on the side of the environmentalists, while Brunetti remains classically aloof. Also, as usual, the pace of the novel is somewhat slow, in keeping with the protagonist. However the book takes you in an unexpected direction, especially in the last 20 pages, even if you are familiar with Leon's style.
And for those really tired of that, there are fewer descriptions of food and Brunetti's kids and wife than usual. While these remain a staple, they seem far less important here. Perhaps that's just a reflection of the more serious tone.