S omewhere beneath Rome the dark figure prowled down a stone ramp into the underground tunnel. The ancient passageway was lit only by torches, making the air hot and thick. Up ahead the frightened voices of grown men called out in vain, echoing in the cramped spaces.

As he rounded the corner he saw them, exactly as he had left them—four old men, terrified, sealed behind rusted iron bars in a stone cubicle.

“Qui êtes-vous?” one of the men demanded in French. “What do you want with us?”

“Hilfe!” another said in German. “Let us go!”

“Are you aware who we are?” one asked in English, his accent Spanish.

“Silence,” the raspy voice commanded. There was a finality about the word.

The fourth prisoner, an Italian, quiet and thoughtful, looked into the inky void of his captor’s eyes and swore he saw hell itself. God help us, he thought.

The killer checked his watch and then returned his gaze to the prisoners. “Now then,” he said. “Who will be first?”