On a gloomy morning in Vigata, a call from Fazio rouses Inspector Montalbano from a nightmare. A man called Giugiu Nicotra has been found dead in the skeletal workings of a construction site, a place now entombed by a sea of mud from recent days of rain and floods. Shot in the back, he had fled into a water supply system tunnel. The investigation gets off to a slow start, but all the evidence points to the world of construction and public contracts, a world just as slimy and impenetrable as mud.

As he wades through a world in which construction firms and public officials thrive, Montalbano is obsessed by one thought: that by going to die in the tunnel, Nicotra had been trying to communicate something.