Stephen had continued throughout 769 and 770 to rely on the support and advice of Christophorus and Sergius who had placed him on the papal throne.
Their antipathy towards the Lombards and general pro-Frankish stance causes King Desiderius to engineer their downfall.
He bribed the Papal Chamberlain, Paulus Afiarta, and other members of the papal court to spread rumors about them to the pope.
When Desiderius attempts to enter Rome in 771 with an army, claiming to be on a pilgrimage to pray at the shrine of St. Peter, Christophorus and Sergius shut the gates of the city against them.
Arriving at the gates and seeing armed troops manning the walls, the Lombard king asks to speak to the Pope, who comes out to him.
During Stephen’s absence, Afiarta and his supporters seek to stir up a mob to overthrow Christophorus and Sergius, but the Primicerius and his son gain the upper hand, and force Afiarta and his colleagues to flee to the Lateran Palace.
Stephen had by this stage returned to the Lateran, and he is confronted in the Basilica of St. Theodore by the fleeing Afiarta and his co-conspirators being chased by Christophorus and his supporters.
Apparently at this point, a suspicious Christophorus, believing that Stephen had entered into some agreement with Desiderius, forces Stephen into taking an oath that he will not turn Christophorus or his son over to the Lombards.
After this, a furious Stephen berates Christophorus, demands he stop harassing Afiarta, and orders him and his followers to withdraw, to which Christophorus complies.
Stephen flees the next day to St. Peter’s Basilica to seek the protection of Desiderius.
The Lombard king, shutting Stephen up in his suites in the Basilica, makes it clear to the Pope that the price for his help is to be the handing over of Christophorus and Sergius.
The Pope sends two bishops to negotiate with Christophorus and Sergius, telling them that they must either retire to a monastery or come out to him at St. Peter’s.
A message is sent at the same time from Desiderius to the people of the city, declaring that Pope Stephen has bid them to expel Christophorus from the city and save themselves from harm.
This message from the Lombard king has the desired effect; Christophorus and Sergius begin to suspect their associates, who in turn rapidly abandon them.
Both are reluctant to leave the city, but eventually both make their way to the Pope during the night.
The next day, Stephen is allowed to return to the city, while Christophorus and Sergius are left in Lombard hands.
Negotiations to secure their release are unsuccessful, and before the day was out, Afiarta arrives with his partisans.
After discussing the situation with Desiderius, they have both men blinded.
Christophorus dies after three days, while Sergius is kept in a cell in the Lateran.
Desiderius, in an attempt to forestall the potential intervention of Charlemagne has Stephen write a letter to the Frankish king, wherein he declares that Christophorus and Sergius had been involved in a plot with an envoy of Charlemagne’s brother, Carloman, to kill the Pope.
Further, that Stephen had fled to Desiderius for protection, and that eventually Christophorus and Sergius were brought out against their will.
While Stephen managed to save their lives, later a group of men had them blinded, but not on Stephen’s orders.
He then concludes that if it wasn’t for “his most excellent son Desiderius”, he would have been in fatal danger, and that Desiderius had reached an agreement with him to restore to the Church all the lands which she had claims on that were still in Lombard hands.
That such a letter was a fiction is demonstrated very soon after; when Stephen asks Desiderius to fulfill the promises he had made over the body of Saint Peter, the Lombard king responds:
”Be content that I removed Christophorus and Sergius, who were ruling you, out of your way, and ask not for rights. Besides, if I do not continue to help you, great trouble will befall you. For Carloman, king of the Franks, is the friend of Christophorus and Sergius, and will be wishful to come to Rome and seize you.”
Desiderius continues to stir trouble in Italy; in 771, he manages to persuade the bishops of Istria to reject the authority of the Patriarch of Grado, and to have them place themselves under the Patriarch of Aquileia, which is directly under Lombard control.
Stephen writes to the rebellious bishops, suspending them and ordering them to place themselves once again under the authority of Grado, or face excommunication.
