Louis XV had decided in 1772 to make Madame du Barry, with whom he was infatuated, a special gift at the estimated cost of 2,000,000 livres.

He had requested that Parisian jewelers Boehmer and Bassenge create a diamond necklace which would surpass all others in grandeur.

It has taken the jewelers several years and a great deal of money to amass an appropriate set of diamonds.

In the meantime, Louis XV has died of smallpox, and du Barry had been banished from court by his successor.

The necklace consists of many large diamonds arranged in an elaborate design of festoons, pendants and tassels.

The jewelers hope it can be a product that the new Queen of France, Marie Antoinette, can buy and indeed in 1778 the new king, Louis XVI, had offered it to his wife as a present, but she had refused.

According to Madame Campan, a French educator and royal lady-in-waiting, the Queen had refused it with the statement that the money would be better spent equipping a man-of-war.

Some said that Marie Antoinette refused the necklace because she did not want to wear any jewel which had been designed for another woman, especially if that woman was a courtesan disliked by the Queen.

According to others, Louis XVI himself had changed his mind.

After having vainly trying to place the necklace outside of France, the jewelers again attempt to sell it to Marie Antoinette after the birth of the dauphin Louis-Joseph in 1781.

The Queen again refuses.

A con artist who calls herself Jeanne de Saint-Rémy de Valois conceives a plan to use the unsold diamond necklace to gain wealth and possibly power and royal patronage.

A descendant of an illegitimate son of Henry II of France, Jeanne de Valois had married an officer of the gendarmes, the soi-disant comte de la Motte, and is living on a small pension which the King had granted her.

In March 1784 she becomes the mistress of the Cardinal de Rohan, a former French ambassador to the court of Vienna.

The Cardinal is regarded with displeasure by Queen Marie Antoinette for having spread rumors about the Queen's behavior to her formidable mother, the late Austrian empress Maria Theresa.

The Queen has also learned of a letter in which the Cardinal had spoken of Maria Theresa in a way that Marie Antoinette found offensive.

At this time, the Cardinal is attempting to regain the Queen's favor in order to become one of the King's ministers.

Jeanne de la Motte, having entered court by means of a lover named Rétaux de Villette, persuades Rohan that she had been received by the Queen and enjoys her favor.

On hearing of this, Rohan resolves to use the "comtesse" to regain the Queen's goodwill.

Jeanne assures the Cardinal that she is making efforts on his behalf.

This begins an alleged correspondence between Rohan and the Queen, the adventuress returning replies to Rohan's notes, which she affirms come from the Queen.

The tone of the letters becomes very warm, and the Cardinal, convinced that Marie Antoinette is in love with him, becomes enamored of her.

He begs Jeanne to arrange a secret nighttime interview for him with the Queen, and the supposed meeting takes place in August 1784.

In the garden of the Palace of Versailles, the Cardinal meets with a woman whom he believes to be the Queen.

This woman is in fact a prostitute, Nicole Lequay d'Oliva, who had been hired by Jeanne because of her resemblance to the Queen.

Rohan offers d'Oliva a rose, and, in her role as the Queen, she promises him that she will forget their past disagreements.

Jeanne de la Motte takes advantage of the Cardinal's belief in her by borrowing large sums of money from him, telling him that they are for the Queen’s charity work.

With this money, Jeanne is able to make her way into respectable society.

Because she openly boasts about her relationship with the Queen, many assume the relationship is genuine.

The jewelers Boehmer and Bassenge resolve to use her to sell their necklace.

She at first refuses a commission, but then changes her mind and accepts it.

According to Madame Campan, the "Queen" had sent several letters to the cardinal, including an order to buy the necklace; they were signed Marie Antoinette de France, but the Cardinal either didn't know or didn't remember that French queens sign with their given names only.

Jeanne de la Motte tells the Cardinal on January 21, 1785, that Marie Antoinette wants to buy the necklace; but, not wishing to purchase such an expensive item publicly during a time of need, the Queen wants the Cardinal to act as a secret intermediary.

A little while later, Rohan negotiates the purchase of the necklace for 2,000,000 livres, to be paid in installments.

He claims to have the Queen's authorization for the purchase, and shows the jewelers the conditions of the bargain in the Queen's handwriting.

Rohan takes the necklace to Jeanne's house, where a man, whom Rohan believes to be a valet of the Queen, comes to fetch it.

Jeanne de la Motte's husband secretly takes the necklace to London, where it is broken up in order to sell the large individual diamonds separately.

Jeanne de la Motte presents the Cardinal's notes when the time comes to pay, but these are insufficient.

Boehmer complains to the Queen, who tells him that she has neither ordered nor received the necklace.

She has the story of the negotiations repeated for her.

Then follows a coup de théâtre.

On August 15, 1785, the Feast of the Assumption, while the court is awaiting the King and Queen to go to the chapel, the Cardinal de Rohan, who is to officiate, is taken before the King, the Queen, the Minister of the Court Breteuil and the Keeper of the Seals Miromesnil to explain himself.

Rohan produces a letter signed "Marie Antoinette de France".

The King, on reading this, becomes furious that Rohan, a prince étranger, could have let himself be fooled, since royalty do not use surnames.

Rohan is arrested and taken to the Bastille; on the way he sends home a note ordering the destruction of his correspondence.

Jeanne is not arrested until three days later, giving her a chance to destroy her papers.

The police arrest the prostitute Nicole Lequay d'Oliva and Rétaux de Villette, who confesses that he had written the letters given to Rohan in the queen's name, and had imitated her signature.

The noted charlatan Cagliostro is also arrested, although it is doubtful whether he had any part in the affair.

The Cardinal de Rohan accepts the Parlement de Paris as judges.

Pope Pius VI is incensed, since he believes that the cardinal should be tried by his natural judge, i. e. himself.

However, his notes remain unanswered.

The Affair of the Diamond Necklace concludes with a sensational trial that results in the acquittal of the Cardinal, of the girl Nicole and of Cagliostro on May 31, 1786.

Nonetheless, Cagliostro is asked to leave France, and departs for England.

Jeanne de la Motte is condemned to be whipped, branded and sent to life imprisonment in the prostitutes' prison at the Salpêtrière. (In June of the following year, she will escape from prison disguised as a boy. In her absence, her husband is condemned to the galleys for life.)

Villette is banished.

Cagliostro, having removed from Paris to London, is accused by the French gutter journalist Charles Theveneau de Morande of being Giuseppe Balsamo, which he denies in his published Open Letter to the English People, forcing a retraction and apology from Morande.