The novel opens with an extended description of the Maison Vauquer, a boarding house in Paris' rue Neuve-Sainte-Geneviève covered with vines, owned by the widow Madame Vauquer. The residents include the law student Eugène de Rastignac, a mysterious agitator named Vautrin, and an elderly retired vermicelli-maker named Jean-Joachim Goriot. The old man is ridiculed frequently by the other boarders, who soon learn that he has bankrupted himself to support his two well-married daughters.
Rastignac, who moved to Paris from the south of France, becomes attracted to the upper class. He has difficulty fitting in, but is tutored by his cousin, Madame de Beauséant, in the ways of high society. Rastignac endears himself to one of Goriot's daughters, Delphine, after extracting money from his own already-poor family. Vautrin, meanwhile, tries to convince Rastignac to pursue an unmarried woman named Victorine, whose family fortune is blocked only by her brother. He offers to clear the way for Rastignac by having the brother killed in a duel.
Rastignac refuses to go along with the plot, balking at the idea of having someone killed to acquire his wealth, but he takes note of Vautrin's machinations. This is a lesson in the harsh realities of high society. Before long, the boarders learn that police are seeking Vautrin, revealed to be a master criminal nicknamed Trompe-la-Mort (Daredevil, literally Cheat-the-Death or Death-Dodger). Vautrin arranges for a friend to kill Victorine's brother, in the meantime, and is captured by the police.
Goriot, supportive of Rastignac's interest in his daughter and furious with her husband's tyrannical control over her, finds himself unable to help. When his other daughter, Anastasie, informs him that she has been selling off her husband's family jewelry to pay her lover's debts, the old man is overcome with grief at his own impotence and suffers a stroke.
Delphine does not visit Goriot as he lies on his deathbed, and Anastasie arrives too late, only once he has lost consciousness. Before dying, Goriot rages about their disrespect toward him. His funeral is attended only by Rastignac, a medical student named Bianchon, a servant named Christophe, and two paid mourners. Goriot's daughters, rather than being present at the funeral, send their empty coaches, each bearing their families' respective coat of arms. After the short ceremony, Rastignac turns to face Paris as the lights of evening begin to appear. He sets out to dine with Delphine, and declares to the city: "À nous deux, maintenant!" ("It's between you and me now!")
