The seventeenth book in Zola's Les Rougon-Macquart series, it is based on the railway between Paris and Le Havre in the 19th century and is a tense, psychological thriller.

The main characters are Roubaud, the deputy station master at Le Havre, his wife, Séverine, and Jacques Lantier.

Lantier is an engine driver on the line and the family link with the rest of Les Rougon-Macquart series.

Lantier is an engine driver with a hereditary madness and has several times in his life wanted to murder women.

Meanwhile, Lantier, who is not working while his engine is being repaired, goes to visit his Aunt Phasie, who lives in an isolated house by the railway.

Finding himself beside the railway track, he sees a figure, on the train coming from Paris, holding a knife, bent over another person.

An investigation is launched and Roubaud and Séverine are prime suspects since they were on the train at the time and were due to inherit property from Grandmorin.

The investigating magistrate, believing that the killer is Cabuche, a carter who lives nearby, dismisses Roubaud and Séverine.

Flore, meanwhile, sees Lantier pass her house every day on the train and noticing Séverine with him realizes they are having an affair and becomes jealous, wishing to kill them both.

One morning she seizes an opportunity when Cabuche leaves his wagon and horses unattended near the railway line.