That was enough to get the man talking, to admit he had gotten the painting from Chaudron, though he said it was Valfiero who had enlisted him and paid his fee. He claimed never to have met Chaudron before that evening, that he had merely been hired for a delivery job and that was all he knew.

“I will let you go unharmed if you promise not to divulge a word of our meeting to Chaudron or Valfiero,” Vincent said. “If you do, I swear to find you and kill you!” Then he walked the man home, noting his address with another threat to his life if he did not keep their meeting a secret.

Now that he was out of prison and free, the nights Vincent had spent watching Chaudron’s apartment and following couriers paid off.

It was dawn when he found the silver-domed house in the seventh arrondissement, where he chose a park bench across from the house and waited. At eight in the morning, a man came out, tall and distinguished in a fine suit, carrying a smart leather briefcase. Vincent followed him for several blocks and into a bank, waited until the man went into an office, then he approached and read the brass plaque on the door: Georges Fournier, Président.

A woman came up behind Vincent and said she was Monsieur Fournier’s secretary and asked what he wanted. He told her nothing. He could not afford to cause a scene. No matter what he said, he knew he would be seen as the man in the wrong, the poor man versus the rich one.

He went back to the same park bench and waited until the end of the day. His stomach growled and his mouth was dry, but he dared not leave his post. Finally, he saw the bank president turn the corner. He rose quickly and made his way to the bottom of the staircase that led to Fournier’s front door. He did not move as the banker came up the path.

Fournier regarded him as if he were nothing more than a beggar. He threatened to call a gendarme, his face filled with annoyance and disgust.

Vincent said only two words, the name “Yves Chaudron,” and though Fournier’s eyes widened, he claimed he had no idea who that was. Still, Vincent did not move.

Fournier threatened to call the police again, and Vincent said, “You should. It will give me an opportunity to tell them about the painting you recently purchased from Chaudron and Valfiero.”

With that, Fournier ushered Vincent inside, past a surprised-looking maid, up a grand staircase and down a hallway into a small library—though he persisted in saying he knew no one named Chaudron or Valfiero.

“If that were true,” Vincent said, “then why have you brought me into your home?” When Fournier did not answer, he said, “The painting you purchased is a forgery.”

“What are you talking about?”

“The painting, the one in your possession, the Mona Lisa, is very likely a fake.”