The Pyramid of Mud by Andrea Camilleri

The Pyramid of Mud is the twenty-second Montalbano mystery from Italy's finest crime writer, Andrea Camilleri.
It's been raining for days in Vigàta, and the persistent downpours have led to violent floods overtaking the Inspector's beloved hometown, sweeping across the land and leaving only a sea of mud behind. It is on one of these endless grey days that a man - a Mr Giuglù Nicotra - is found dead. His body discovered in a large sewage tunnel, half naked and with a bullet in his back.
The investigation is slow and slippery to start with, but when Montalbano realizes that every clue he uncovers and every person he interviews is leading to the same place: the world of public spending - and with it, the Mafia - the case begins to pick up pace.
But there's one question that keeps playing on Montalbano's mind: in his strange and untimely death, was Giuglù Nicotra trying to tell him something?