Florent, who was deported in 1848, returns to Paris illegally 8 years later. The novel tells the story of how he is taken in by his brother and absorbed into the life of Les Halles as a fish inspector and then vomited out again as an agitator to be deported back to Cayenne.
Much more than this it is a vivid picture of life in the new food markets of Paris. The descriptions of food and characters and streets take you to the place in a cinematic way that is breath-taking.
As part of Zola's naturalism observations, it looks at and ridicules the falseness of the bourgeois shop keepers.