The Kingdom of France helped the Venetians who fought against the Ottoman Empire in Crete during the reign of King Louis XIV. The Ottomans learned that France was secretly helping Venice even if they claimed to be friendly to the Ottoman Empire. However, it was not easy to prove this truth as the French Embassy was using a secret code to prevent the deciphering of their letters. There were very few people who know this code. Köprülü Mehmed Pasha, who was the grand vizier from 1656 to 1661, had the code broken in a very interesting way.

Köprülü Mehmed Pasha was looking for an opportunity to pay off a disrespect from La Haye, who was the French ambassador to Istanbul. This opportunity came to Mehmed Pasha by itself at an unexpected time. A French soldier named Vertamont, who served at the war in Crete in 1658, presented an important gift to the pasha - a package of encoded letters that were entrusted to him by the captain so that he could deliver them to Venice's Ballarino and the French ambassador. Vertamont obtained the necessary permission from his country to visit Istanbul and was written a passport. The French government gave the encoded letters for La Haye, to him. However, Vertamont gave these letters to the district governor in Istanbul instead of La Haye and said that he wanted to be a Muslim.

The district governor sent Vertamont to the grand vizier who was in Edirne, and he was interrogated. In the interrogations, he confirmed the collaboration between Venice and France in Crete and informed that La Haye was secretly helping the Venetians.

As evidence to what he said, he delivered the letters he had to the grand vizier, but the code could not be broken.

French ambassador in the dungeon

Köprülü Mehmed Pasha had La Haye brought to Edirne after he recovered. The ambassador was also interrogated there. He was asked what was written in the letters but the ambassador told that he could not break the code by himself and the translator of the embassy had gone to France six months before. Then, the grand vizier ordered him to be sent to the dungeon together with his son. Then, the grand vizier campaigned for Transylvania with the army. Until he returned from the campaign, the ambassador and his son were kept in the dungeon. When the victorious grand vizier came back from campaign to Edirne, people entrusted to request La Haye and his son's release came. The grand vizier's replied: "Gosh! Are they still here?" and ordered their release. La Haye and his son were released and they left the city. However, the grand vizier did not stop following the father and son. He reported their improper behaviors to France through a sergeant. La Haye was dismissed. After he was dismissed, La Haye was kept in the dungeons of Yedikule for some more days since a French ship left from Istanbul with goods from the empire, although it was forbidden. The departure of the ship coincided with the days when he would leave the city. Therefore, he was also seen as responsible for it and was punished. The now former ambassador was released from the dungeon after paying a fine and he returned to France in 1660.

The French allied with Austria

Louis XIV would help the Austria against the Ottoman Empire even though the Austrians were their number one enemies. Grand Vizier Fazıl Ahmed Pasha conquered Uyvar in the Austro-Turkish War in 1663. Vienna might also have been conquered as its walls and fortifications were weak. The Ottoman army confronted the Austrian army in Sengator. The Ottomans had the upper hand at the beginnings of the battle, but Austria received help from an unexpected ally for this battle. The intervention of French troops saved Austria from defeat and turned the war against the Ottomans.

Encoded letters

Vertamont gave the encoded letters about the French help to Venice to the Ottomans. While they tried to break the code in Edirne, La Haye was breaking out in a cold sweat in Istanbul. He heard that the grand vizier had the letters. He immediately met with the officials of the embassy and discussed how they should act from now on. In this meeting, the code translator who was responsible for deciphering letters was scared most since the grand vizier earlier had tortured him by caning the soles of his feet when he did not decipher a letter. The French code translator he said: "Monseigneur, I am worried about my nature. If I get a beating, I can reveal all secrets. Either hide me or abduct me." The mood of the code translator bothered La Haye, and in the meeting, it was decided that the translator would be hidden somewhere safe.

Ottoman officials tried to break the code for days but they could not. Then, Köprülü Mehmed Pasha ordered La Haye to Edirne. When La Haye got the order, he was very sick with kidney stones. He could not get out of the bed and sent his son Denis de La Haye on his behalf. The grand vizier did not welcome Denis de La Haye warmly. His bold words tried the pasha's patience. Mehmed Pasha sent only Denis from the embassy committee to the dungeon and asked others to break the code, warning them that they would be killed if they did not do it. However, no one could solve them.

While the committee was driven into a corner in Edirne, the ambassador did not idle.

A rumor at the embassy bothered him. According to this rumor, a Frenchman named Quiclet, who knew how to break the codes, was getting ready to go to Edirne. Hearing this, La Haye invited Quiclet to the embassy and interrogated him for a few hours on the terrace. After the interrogation, the terrace exploded with a gesture by La Haye after he went out. Quiclet fell through to the ground from the explosion but did not die. The officials in the embassy saw it, finished Quiclet off and secretly buried him.