The narrative details many of Le Bon Marché's innovations, including its mail-order business, its system of commissions, its in-house staff commissary, and its methods of receiving and retailing goods.

Like its predecessor, Au Bonheur des Dames focuses on Octave Mouret, who at the end of the previous novel married Caroline Hédouin, the owner of a small silk shop.

The novel tells the story of Denise Baudu, a 20-year-old woman from Valognes who comes to Paris with her younger brothers and begins working as a saleswoman at the department store "Au Bonheur des Dames".

Denise's story is played against the career of Octave Mouret, the owner of Au Bonheur des Dames, whose retail innovations and store expansions threaten the existence of all the neighborhood shops.

Under one roof, Octave has gathered textiles (silks, woolens) as well as all manner of ready-made garments (dresses, coats, lingerie, gloves), accessories necessary for making clothes, and ancillary items like carpeting and furniture.

Massive advertising, huge sales, home delivery, and a system of refunds and novelties such as a reading room and a snack bar further induce his female clientele to patronize his store in growing numbers.

In Au Bonheur des Dames, he uses a young widow to influence a political figure–modeled after Baron Haussmann–in order to gain frontage access to a huge thoroughfare, the present day rue de Quatre-Septembre, for the store.