A luminous spring day in Venice, and Commissario Brunetti and Ispettore Vianello take a break from the Questura to come to the rescue of Vianello's friend Marco, who has been arrested while protesting against chemical pollution of the Venetian lagoon. They suceed in securing Marco's release uncharged, only to be faced by the fury of his father-in-law, owner of a glass factory on the island of Murano. The old man is seething with rage at his son-in-law, and his daughter shares with Brunetti her fear that he will actually harm her husband. But it is not Marco who has uncovered the guilty secret of the glass foundries, nor his body that 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 island and fouling the waters of the laguna. A man is dead – but will politics and expedience protect the killer from the law?