The Charterhouse of Parma tells the story of the young Italian noble Fabrizio del Dongo and his adventures from his birth (in 1798) to his death in 1829 (?). Most of the novel is set in a fictionalized town of Parma while his early years are spent in a castle on Lake Como (both in modern-day Italy).
The novel's early section is largely focused on Fabrizio's rather quixotic effort to join Napoleon when he returns to France in March 1815 (the Hundred Days). Fabrizio is a young man, rather naive, and doesn't speak very good French. However, he won't be stopped and he leaves his home on Lake Como and travels north under false papers. He wanders through France, losing money and horses at a fast rate. He is nearly imprisoned as a spy but he escapes, dons the uniform of a dead French Hussar and, much to his surprise, ends up traveling into the Battle of Waterloo.
Stendhal, a veteran of many battles during the Napoleonic period (he was one of the few survivors of the retreat from Russia in the 1812), describes this famous battle as a chaotic affair with soldiers who gallop one way, then another, while bullets plow the fields around them. Fabrizio is lucky to survive the fighting with serious wound to his leg (given to him by one of the retreating French cavalry men) and he returns to his family castle, injured, broke, and still wondering "was I really in the battle?". Towards the end of the novel his efforts, such as they are, lead people to say that he was one of Napoleon's generals.
Having returned to Lake Como the novel now divides its attention between Fabrizio and his aunt (his father's sister), Gina, the sometime Duchess of Sanseverina. Gina meets and falls in love with the Prime Minister of Parma, Count Mosca. Count Mosca proposes that Gina marry a wealthy old man, who will be out of the country for many years as an ambassador, so she and Count Mosca can be lovers while living under the social rules of the time. Gina's response is: "But you realize that what you are suggesting is utterly immoral?". She agrees and so a few months later, Gina is the new social eminence in Parma's rather small aristocratic elite.
Ever since Fabrizio returned from Waterloo, Gina has had very warm feelings for her nephew, and she and Count Mosca try to plan out a successful life for the young man. Count Mosca's plan has Fabrizio go to seminary school in Naples, when he graduates, he will come to Parma and be installed as a senior figure in the religious hierarchy, soon to be the Archbishop as the current office-holder is old. The fact that Fabrizio has no interest in religion (or celibacy) matters not to this plan. Somewhat oddly (to the modern reader) Fabrizio agrees to the plan and leaves for Naples.
The book then describes in great detail how Gina and Count Mosca live and operate in the court of the Prince of Parma (named Ranuce-Erneste IV). Stendhal, who spent decades as a professional diplomat in northern Italy, gives a lively and surprisingly interesting account of the court, though all of what he describes is entirely fictional as Parma was (during the time of the novel) ruled by Marie Louise, Duchess of Parma. So much attention is given to Gina and Count Mosca that some have suggested that these two are the true heroes of the novel.
After several years in Naples, during which Fabrizio has many affairs with local women, he returns to Parma and shortly gets involved with a young actress whose manager/lover takes offense and tries to kill Fabrizio. In the resulting fight, Fabrizio kills the man then flees Parma; fearing, rightly, that he will not be treated justly by the courts. However, his efforts to avoid capture are unsuccessful and he is brought back to Parma and put at the top of the tallest tower in the city, in a jail cell. His aunt, Gina, in great distress at what she feels is Fabrizio's certain death, goes to beg the Prince for his life. The Prince wants Gina to offer herself to him in exchange for Fabrizio's freedom and is non-plussed when she refuses to agree to his implied offer.
For the next nine months Gina schemes to have Fabrizio freed and manages to get secret messages relayed to him in his tower. The Prince keeps hinting that Fabrizio is going to be executed (or poisoned) as a way to put pressure on Gina. Meanwhile, Fabrizio is oblivious to his danger and is living happily because he has fallen in love with the commendant's daughter Clelia Conti. Fabrizio sees Clelia nearly every day as she tends to her birds and she falls in love with him and after some time the he persuades her to speak with him with the help of ABC, made of sheets, which ripped from one of the books, he was allowed to read (something like e pre-modern keyboard).
Gina finally gets Fabrizio out of his prison (with the aid of a very long rope and the help of Clelia). The only thing that concerns Fabricio is, whether he could meet Clelia, after he escapes from the citadel. But Clelia who has sacrificed the health of her father because of her beloved man, promises the Virgin Mary, that she shall never see Fabricio, if her father gets well and will do anything that he say.
Gina leaves Parma and puts in motion a plan to have the Prince of Parma assassinated. Count Mosca stays in Parma and when the Prince does die (perhaps poisoned by Gina's poet/bandit/assassin) he puts down an attempted revolt by some local revolutionaries and gets the son of the Prince installed on the throne. Clelia, to help her father who was disgraced by Fabrizio's escape, marries a wealthy man and so she and Fabrizio live unhappily for some years because of the promiss she made.
Fabrizio voluntarily returns to the Farnese Tower to see Clelia and is almost poisoned there. To save him, Gina promises to give herself to the new Prince. She keeps her promises, but immediately leaves Parma afterwards. Gina never returns to Parma but she marries Count Mosca.
Once he is declared innocent of the crime of murder, Fabricio assumes his duties as a powerful man of the Catholic Church and a preacher whose sermons become the talk of the town. The only reason for these sermons, as Fabricio says, is to see Clelia and to speak with her. After 14 months of suffer for the both, she agrees to meet with him every night, but the only condition she lays down is that she never meets him in the daylight in order to keep her promiss, or else they would be both punished for her sin. A year later she bears Fabricio's child. When the boy is 2-years-old Fabricio insists, that he should take care of him in the future, because he is feeling lonely and suffers that his own child won't love him. The only solution to take the child is that Clelia simulates its illness and death. Later the child does die and after several months Clelia dies too. After her death Fabricio retires in the charterhouse of Parma, which gave the book its title, where he spends less than a year. Shortly after the countess Mosca, Gina dies.