In the aftermath of a shooting in Naples, Matteo sees all reason to exist crumble. His little boy is dead. His wife, Giuliana, has disappeared. He himself sinks into loneliness and, night after night, in his empty cab, roams the city streets for no reason. But one evening, he lets a strange customer into the car, who offers him a drink in a tiny café as payment for his fare. There, Matteo meets the owner, Garibaldo, the unrepentant priest Don Mazerotti, and above all Professor Provolone, a colorful character, as erudite as he is sulphurous, who makes strange speeches about the reality of the Underworld. And he claims that you can go down there...