The first third of the novel provides a lengthy exploration of the characters' histories. Balzac makes this clear after 150 pages: "Ici se termine, en quelque sorte, l'introduction de cette histoire." ("Here ends what is, in a way, the introduction to this story.")[20] At the start of the novel, Adeline Hulot – wife of the successful Baron Hector Hulot – is being pressured into an affair by a wealthy perfumer named Célestin Crevel. His desire stems in part from an earlier contest in which the adulterous Baron Hulot had won the attentions of the singer Josépha Mirah, also favored by Crevel. Mme. Hulot rejects Crevel's advances. The Baron has so completely lavished money on Josépha that he has borrowed heavily from his Uncle Johann – and, unable to repay the money, the Baron instead arranges a War Department post in Algeria for Johann, with instructions that Johann will be in a situation in that job to embezzle the borrowed money. The Hulots' daughter, Hortense, has begun searching for a husband; their son Victorin is married to Crevel's daughter Celestine.
Mme. Hulot's cousin, Bette (also called Lisbeth), harbors a deep but hidden resentment of her relatives' success, especially of Hortense 'stealing' Bette's intended sweetheart. A peasant woman with none of the physical beauty of her cousin, Bette has rejected a series of marriage proposals from middle-class suitors who were clearly motivated by her connection to the Hulots, and remains unmarried at the age of 42. One day she comes upon a young unsuccessful Polish sculptor named Wenceslas Steinbock, attempting suicide in the tiny apartment upstairs from her own. As she nourishes him back to health, she develops a maternal (and romantic) fondness for him. At the beginning of the story Bette is living in a modest apartment in a lodging house shared by the Marneffe couple, both of whom are ambitious and amoral. Bette befriends Valérie (nee Fortin), the young and very attractive wife of a War Department clerk, Jean-Paul-Stanislas Marneffe; the two women form a bond to attain their separate goals – for Valérie the acquisition of money and valuables, for Bette the ruination of the Hulot household by means of Valérie's luring both the Baron and Steinbock into infidelity and financial ruin.
Baron Hulot, meanwhile, is rejected by Josépha, who explains bluntly that she has chosen another man because of his larger fortune. Hulot's despair is quickly alleviated when he visits Bette in her lodging and there meets and falls in love with Valérie Marneffe. He showers her with gifts, and soon establishes a luxurious house for her and M. Marneffe, with whom he works at the War Department (Bette joins them in their new home, to serve as an excuse for the Baron's visits). These debts, compounded by the money he borrowed to lavish on Josépha, threaten the Hulot family's financial security. Panicked, he convinces his uncle Johann Fischer to quietly embezzle funds from a War Department outpost in Algiers. Hulot's woes are momentarily abated and Bette's happiness is shattered, when – at the end of the "introduction" – Hortense Hulot marries Wenceslas Steinbock.
Crushed at having lost Steinbock's as her intended spouse, Bette swears vengeance on the Hulot family. Her strategy is to work on Baron Hulot's demonstrated weakness for acquiring and lavishing more money than he has on young mistresses. Soon the Baron is completely besotted – and financially over-extended – with Valérie, and completely compromised by repeatedly promoting her husband within the Baron's section of the War Department. Before long, Bette has already contrived to have Crevel and Steinbock also ensnared by Valérie's charms. Hortense discovers Steinbock's infidelity and returns to her mother's home. Before long, the Baron's misconduct becomes known to the War Department; Uncle Johann is arrested in Algeria and commits suicide, the Baron is forced to retire suddenly, his brother, a famous war hero, saves him from prison and then quickly dies of shame over the family disgrace. The Baron deserts his family and hides from his creditors. It appears that Valérie, soon a widow, will marry Crevel and thus gain entrance to the Hulot family as Celestine's mother-in-law. In short, the family is devastated by these repeated blows – and Bette's machinations are completely concealed from them.
