It is a luminous spring day in Venice, as Commissario Brunetti and Inspettore Vianello take a break from the Questura to come to the rescue of Vianello's friend Marco Ribetti, who has been arrested while protesting against chemical pollution of the Venetian lagoon, only to be faced by the fury of Marco's father-in-law, owner of a glass factory on the island of Murano.

But it is not Marco who has uncovered the guilty secret of the polluting glass foundries of the island of Murano, nor he whose body is found dead in front of the furnaces which burn at 1400 degrees, night and day. The victim has left clues in a copy of Dante and Brunetti must descend into an inferno to discover who is burning the land and fouling the waters of the lagoon...