One day, Monsieur Defarge enters his shop with the mender of roads and takes him to the attic with the three "Jacques." The mender of roads tells his story: he had watched a man clinging to the underside of Marquis Evrémonde's carriage, and about a year later saw soldiers escort the same man, who was accused of killing the Marquis, to prison. A petition to save the man's life was presented to the King and Queen, but to no avail. The man was hung on a gallows above the village fountain. The mender of roads explains how the corpse cast a long and frightening shadow.
In presenting a petition, the commoners are working within the established political structure: accepting the nobles as rulers and making an appeal to their mercy. But the nobles squander their chance to show mercy, and hang the murderer as a warning. The effect is the opposite: the dead man's shadow represents the commoner's desire for revenge and revolution. By showing no mercy the nobles give up any chance of receiving any mercy.
Defarge sends the mender of roads outside and consults with the Jacques. Jacques Three, hungry for blood, agrees with Defarge that the Marquis's castle and the entire Evrémonde race should be exterminated. Another Jacques points to Madame Defarge's knitting, which lists in its stitching the names of everyone the revolutionaries mean to kill.
Just as the Marquis would exterminate the people, those people would exterminate him. In other words, the revolutionaries are just as blood-minded as the corrupt and brutal aristocracy they seek to overthrow.
Several days later, Monsieur and Madame Defarge take the mender of roads to Versailles to see a procession of the King and Queen. The mender of roads, overwhelmed with excitement, shouts "Long live the King!" Defarge thanks the man for helping to keep the aristocrats unaware of the people's rage.
The mender of roads exemplifies the fickle mob, who crave spectacle above all else. One minute he's working for the Revolution, the next he's overcome with joy at seeing the king. The Defarges exploit people like him.