The Sieur Louis de Conte, a fictional character invented by Mark Twain, tells the story of Joan of Arc, Louis' childhood friend and an actual figure in history, who fights for French independence from the English in the 15th century. Louis accompanies Joan as her secretary through the battles and witnesses her trial and execution at the hands of the English.

Joan of Arc grows up in Domremy, a small village in the eastern part of France. Armagnacs, or French loyalists, populate her village in an area dominated by Burgundians, or English sympathizers. Her life proceeds normally until she hears voices from saints and angels who urge her to fight for French independence from the English.

She must first convince the governor of Vaucouleurs to provide her with an armed escort to Chinon, where Charles VII resides, the dauphine of France. The governor refuses, but Joan persists until he agrees to provide the armed escort. Only sixteen years old, Joan leaves for Chinon with veteran knights, Louis the narrator and several of her childhood friends.

The issue of Joan hearing voices garners an inquisition from the Roman Catholic Church, presided over by French clergymen. Joan answers all questions satisfactorily, and she is set free to do whatever she can for France. The inquisition also allows her to wear men's clothing, as women's attire is not appropriate for her tasks.

While at court in Chinon, Joan sees through an imposter substitution ruse and persuades the genuine Charles VII to make her the leader of the entire French army. She leads the army to a successful campaign against the English at Orleans, which is under siege, by using aggressive attack strategies rather than the passive tactics to which the French are accustomed. Afterwards known as the Maid of Orleans, Joan secures the road to Rheims, thereby enabling the coronation of Charles VII as the King of France. She then attempts to take Paris, but is pulled back due to political treachery. During her military career Joan also fights and wins the battle of Patay, a turning point in the Hundred Years' War.

While on a minor campaign to free the town of Compiegne, Joan encounters the English and her personal guard defends her, although surrounded. With all her personal guard killed or wounded, the English capture Joan. She tries to escape twice and fails each time. The English move her to Roen where she defends herself from the Catholic prosecutor, Pierre Cauchon, the Bishop of Beauvais.

Cauchon must obtain a confession from Joan because she thwarts his efforts to trick her during several trials. His purpose is to prove Joan a criminal against the Roman Catholic Church in order not to make her a French martyr. He finally resorts to wearing Joan down physically until she signs a false confession. The English then burn Joan at the stake; however, the goal of not making her a martyr fails.

Mark Twain's story about Joan of Arc is historical fiction because he fleshes out probable scenes and adds other fictional characters. This makes for an entertaining story based on historical fact, but not a biography in the strict sense of the genre.