The story takes place in Paris in the year 1819, in a decrepit, dirty, ill-smelling boardinghouse on the left bank of the Seine.
Mme. Vauquer, a stingy old widow who owns the place, rules over her tenants. They are people with modest means and desires, like Mlle. Michonneau, the old maid; Poiret, a puppet-like human being; and a young orphan, Victorine Taillefer. Three tenants stand out in this company: Eugène de Rastignac, a young student from the provinces, of noble origin, but poor and eager to try his luck in the capital; Vautrin, the "strong" man, bon vivant and humorous, but mysterious and alarming; and Père Goriot, a retired merchant, who seems to be suffering from a mysterious sorrow.
Rastignac soon discovers that strange events are taking place at the seemingly respectable boardinghouse: Old Goriot pressing silver dishes into ingots, Vautrin furtively returning to the house in the middle of the night in spite of the bolted doors, Goriot being visited by pretty girls whose bills he pays.
Rastignac is going to find out the solution of one of the mysteries. Pursuing his ambitions, he manages to be introduced into Parisian high society with the help of his influential cousin, Mme. de Beauséant. Everything seems to be working according to his plans, but for mentioning the name of Goriot, he finds himself shut out of the Countess de Restaud's salon, the meeting place of the cream of society. Crestfallen over his first faux-pas, he learns from Mme. Beauséant the secret of Père Goriot's life. The old man has ruined himself and has accepted a miserable life in order that his two daughters might be wealthy. Anastasie has married a nobleman, Count de Restaud; Delphine an Alsatian banker, Baron of Nucingen. Goriot, welcomed as long as his fortune had lasted, found himself ostracized by his sons-in-law when he became poor.
Vautrin, who has sensed ambition in Rastignac, cynically offers him a bargain: The young student should win the love of the fair Victorine, whose father is extremely rich but who has disowned her. As the only obstacle to Victorine's inheriting the fortune is her brother Frederic, Vautrin for the sum of 200,000 francs would manage to get rid of young Taillefer, thus insuring Victorine's and Rastignac's fortune. Rastignac is indignant, but one feels that he is secretly tempted by the proposal.
After Rastignac's failure in high society, he will try, aided by his cousin, to conquer the "middle world." He is introduced to Mme. de Nucingen and, with the help of Goriot, soon becomes her lover. In the meantime, Vautrin has started his Machiavellian plan and has Victorine's brother murdered. Everything seems to be in his favor when Mlle. Michonneau, a spy for the police, discovers Vautrin to be an escaped convict and has him arrested. This ends the detective story.
Goriot's daughters come to him for help. Their husbands have discovered their affairs and are trying to ruin them. In a pathetic scene, the two daughters show their monstrous egoism and pride. Père Goriot is afflicted by a stroke. He soon becomes delirious, muttering incoherent words, revealing also his extreme love for the daughters who have left him, one to go to a dance, the other to protect her fortune.
Goriot dies blessing his daughters, with only Rastignac and Bianchon, a medical student, at his bedside. Rastignac attends to the funeral arrangements and, after saying a last goodbye to Goriot in the graveyard overlooking Paris, declares war on the capital: "Beware, Paris, here I come" and goes to Mme. de Nucingen's for dinner.