Last week we left the Marques de Valfierno and Yves Chaudron in Mexico City awash in fake Murillo paintings. Chaudron was the faker, his partner the seller.

Chaudron became bored with painting so many replicas of the same painting. To keep up with Valfierno’s galloping success, he began hiring Mexican painters to do his work.

It was not a good move. The Mexicans were too talkative to fit into such a well-oiled confidence scam. As work leaked out, grifters and crooks tried to muscle in. That crumbled the cookie. Valfierno and Chaudron took off for Paris, loaded with their loot from Buenos Aires and Mexico City.

In France every year, scores of questionable works by Jean Baptiste Camille Corot, Jean François Millet, Titian, and others were sold, overcrowding the fakery market. Valfierno, swollen with pride, yearned to do something more prestigious, lucrative, and daring.

He set about engineering the supreme coup in art forgery.

From the crowd of confidence men Valfierno knew, he recruited three: a monocled Englishman of impressive nonchalance, a Frenchman who had all the right connections, and an American who knew a sizable percentage of those listed in the Social Register.

The ring set up headquarters in a villa not far from the Place de l’Etoile. Their target area included a score of the most expensive hotels in Paris. They entertained lavishly — apéritifs, fine French cuisine and wines, champagne, Napoléon brandy is large snifters, rich Havana cigars. As hosts, the four men were carefully careless talkers, given to intimations, nonchalant innuendos, blatant boastings.

They could do anything for a friend. The friend had only to ask. Did he need a string pulled in the French bureaucracy? Did he want to meet the glittering star of the Folies Bergère?

The delivery of these precious services quickly certified the conspirators’ skill and reliability. Valfierno’s crew began selling little things from the Louvre. Nothing was actually ever stolen, although the buyers thought otherwise.

A buyer who expressed interest in a particular painting and was willing to pay an appropriate price soon found it delivered with a sheaf of Louvre documents to his doorstep, usually outside of France.

The dossier always included at least one marked “secret,” which stated that the painting was missing but, to suppress public scandal, had been replaced by a replica.

For three years the ring sold fine things from the Louvre.

Then one night when the four men and a greedy collector were very far along the champagne trail, one of the ring boasted that they might steal the Mona Lisa for their guest.

“Why not?” the American suggested.

Valfierno and the others expected a rebuff from their guest. They were stunned by his outrageous response to their jest.

“Why not?” the collector repeated. “It has never been done, but that is no reason it could not be done, and knowing Paris as you do, you should be able to manage it.”

Chaudron began making more frequent trips to the Louvre to study a single painting, Mona Lisa.

Valfierno’s ring had several ambiguities working for them. There had long been a question about the authenticity of the Louvre painting — or at least its uniqueness. Some thought da Vinci had painted it at least twice. Recently this idea has made headlines.

Whatever the battle might be among experts, the ring could not sell any Chaudron copy as along as the Mona Lisa hung in the Louvre.

According to a confession made by Valfierno to Karl Decker in a Casablanca saloon in 1914 and finally published in The Saturday Evening Post in 1932, after Valfierno and Chaudron were dead, Valfierno hired an Italian, Vincenzo Perugia, to steal the painting. An employee of the Louvre, Perugia had worked for Valfierno before, but he knew nothing of the forgeries.

Meanwhile, Valfierno and his cronies were quietly striking bargains for the eventual delivery in America of the one-and-only real Mona Lisa.

Mondays are cleaning days in the museum, when it is closed to the public. Except on crowded weekends and holidays, in the Louvre and Prado and other famed museums, copyists are allowed to set up easels so they can study and try to replicate Old Masters.

They are not allowed to make their copies in the same size as the originals. Storage closets are provided so that copyists don’t have to trundle their easels, camp stools, canvases, and paints in and out of the museum for every session.

Like other copyists, Chaudron set himself up every day in front of the Mona Lisa and painted her. At this point he was not painting a replica to sell but was seeking the best way to successfully counterfeit the original.

The original was painted on a wood panel, and Chaudron found panels of appropriate age and size. Slowly he began making a faithful replica. After he finished it, he painted another, and then another.

When the first copy was completed, it was quietly shipped to the United States and made it through Customs declared as a copy. Others followed. Their presence was kept secret.

By the time Chaudron had finished six new Mona Lisas, the ring decided that it could not delay much longer in delivering the original. Max Friedlander, one of the most respected art experts of the day, once observed, “Forgeries must be served hot as they come from the oven.”

About 4:00 P.M, Sunday, 20 August 1911, Perugia and two other men entered the crowded museum, mingled with the visitors, and when the coast was clear, hid themselves in the copyists’ closets, where they remained long after the museum was cleared and closed for the day.

Early Monday morning when the maintenance crews began work, Perugia and his helpers slipped into Louvre workmen’s smuggled garb and pretended to be busy with assigned tasks. Unfortunately, Picquet, the head workman, was caught up in some repairs in the Grand Gallery, adjacent to the Salon Carré, the fabled painting’s home and where Napoleon had married Josephine.

He was in and out constantly, and Perugia could do nothing until Picquet went off to another part of the museum.

While working in the museum, Perugia had helped cobble the shadow box and frame that displayed the painting. He knew exactly how much it weighed and how it was attached to the wall.

At 7:20 the thieves unhooked their prize and began carrying it off. Three men carrying a painting on a working day was not something unusual. Once they entered a stairway used only by staff, they paused to remove the wood panel and abandoned the framing ensemble.

Then disaster struck. Valfierno had used a wax impression to make a key for a stairway door they had to go through. Perugia had never tested it. It did not work. Furious, Perugia yanked a screwdriver from his pocket and set about stripping the lock itself. He had removed the bronze knob and was twisting out the next screw when his accomplice outside the Salle de Sèpt Metres whistled. Someone was coming.

Perugia dropped the knob into his pocket and hid the painting under his workman’s cover. The intruder happened to be the museum plumber. Perugia lost no time complaining that someone had swiped the doorknob and he couldn’t open the door. The plumber obligingly took out his key and unlocked the door and went on his way.

The men went the rest of the way down the stairs and found a wide open door to the street. The guard had gone off to get a bucket of water to wash the vestibule. A car was waiting. Within 15 minutes painting and thief were in the ring’s headquarters, after completing the art heist of the century.

The theft of Mona Lisa was not discovered until the next day, Tuesday. At 9:00 A.M. a painter named Louis Beroud arrived. He was painting a picture of the Salon Carré itself and complained about the absence of the da Vinci. Brigadier Poupardin, the head of the Louvre guards, assured him that the painting must have been removed for photographing. Beroud asked again when Poupardin passed through at noon.

When Poupardin checked with the photography studio, he learned the painting was not there. An alarm was passed upwards through the chain of bureaucratic channels until it reached the acting head of the museum. The Louvre immediately went into lockdown. Every nook and cranny was searched.

Of course, nothing was found but the abandoned detritus.

Sensational stories filled the press, as a chain of official inquiries escalated in the museum and the French government. Heads rolled.

The scandal was great news for Valfierno and his gang. They quickly sold “the real Mona Lisa” to their larcenous buyers, who would never be able to let anyone else ever see their prize.

Many years later the story floated in Paris that a certain well-known American collector, whom I will not identify, was offered “the stolen Mona Lisa” by two different intermediaries. Not being able to tell which of the two was the genuine stolen painting and which was the fake, and unable to consult an expert, he purchased them both.