Detective Montalbano

As torrential rain pours down on Vigata, a plastic bag containing a body cut into pieces is found in a clay field. All the signs point to an old-fashioned Mafia killing. But why is Montalbano's trusted colleague and friend Mimi Augello suddenly irritable and short-tempered, and why is he insisting that the investigation be assigned to him? Could Mimi somehow be involved in the case?