La Bête humaine (English: The Beast Within or The Beast in Man) is an 1890 novel by Émile Zola. The story has been adapted for the cinema on several occasions. 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. He is the son of Gervaise (L'Assommoir), the brother of Étienne Lantier (Germinal) and Claude Lantier (L'Œuvre) and the half-brother of the eponymous Nana.

Lantier is an engine driver with a hereditary madness and has several times in his life wanted to murder women. His relationship with his engine, La Lison, provides some degree of control over his mania.

As a result of a chance remark, Roubaud suspects that Séverine had an affair years earlier with Grandmorin, a director of the railway company, who acted as her patron and helped Roubaud get his job. He forces a confession out of her and makes her write a letter to Grandmorin telling him to take a particular train that evening, the train Roubaud and Séverine are taking back to Le Havre.

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. On leaving he meets his cousin, Flore, with whom he has a mutual attraction. After a conversation, his passions become inflamed and he is on the verge of raping her. This, in turn, brings on his homicidal mania. He desires to stab her but just about controls himself and rushes away. Finding himself beside the railway track, he sees a figure, on the train coming from Paris, holding a knife, bent over another person. He later finds the body of Grandmorin beside the track with his throat cut, robbed of his watch and some money.

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. Lantier sees Roubaud while waiting to be interviewed and identifies him as the murderer on the train but when questioned says he cannot be sure. The investigating magistrate, believing that the killer is Cabuche, a carter who lives nearby, dismisses Roubaud and Séverine.

Despite their being cleared of suspicion, the marriage of Roubaud and Séverine declines. The money and watch stolen from Grandmorin are actually hidden behind the skirting board in their apartment, as Roubaud is the murderer. Séverine and Lantier begin an affair, at first clandestinely but then more blatantly until they are caught by Roubaud. Despite his previous jealousy, Roubaud seems unmoved and spends less and less time at home and turns to gambling and drink.

Séverine admits to Lantier that Roubaud committed the murder and that together they disposed of the body. Lantier feels the return of his desire to kill and one morning leaves the apartment to kill the first woman he meets. After having picked a victim, he is seen by someone he knows and so abandons the idea. He then realizes that he has the desire no longer. It is his relationship with Séverine and her association with the murder that has abated his desire.

One day, Séverine realizes that Roubaud has taken the last of their hidden money. Lantier has the opportunity to invest money in a friend's business venture in New York. Séverine suggests they use the money from the sale of the property they inherited from Grandmorin. Roubaud is now the only obstacle to this new life and they decide to kill him. They approach him one night when he is working as a watchman at the station, hoping that the murder will be attributed to robbers. At the last moment, however, Lantier loses his nerve.

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. She hatches a plot to remove a rail from the line in order to cause the derailment of his train. One morning she seizes an opportunity when Cabuche leaves his wagon and horses unattended near the railway line. She leads the horses onto the line before the train arrives. In the resulting crash numerous people die and Lantier is seriously injured. Séverine, however, remains unhurt. Wracked by guilt, Flore commits suicide by walking in front of a train.

Séverine nurses Lantier back to health. She convinces him that they must kill Roubaud, and they concoct a plan to get away with it. However Lantier's mania returns, and when Séverine tries to make love with him, just before Roubaud is due to arrive, he murders her. The unfortunate Cabuche finds Séverine's body and is accused of killing her at the behest of Roubaud. Both are put on trial for this and the murder of Grandmorin. They are both convicted and sentenced to life imprisonment.

Lantier begins driving again, but his new engine is just a number to him. He begins an affair with his fireman's girlfriend.

Lantier then drives a train carrying troops towards the front at the outbreak of the Franco-Prussian War. The resentment between Lantier and his fireman breaks out as the train is travelling at full steam. Both fall to their deaths as the train full of soldiers hurtles driverless through the night.

• 1890, La Bête humaine (French), Paris: Bibliothèque-Charpentier
• 1901, The Monomaniac, translated and edited with a preface by Edward Vizetelly, London: Hutchinson & Co
• 1956: The Beast in Man, translated by Alec Brown (Elek)
• 1968, The Beast in Man (translated by Robert Godfrey Goodyear and P.J.R. Wright), London: Signet Classic
• 1977, La Bête humaine (translated by Leonard Tancock), London: Penguin, ISBN 978-0-140-44327-1
• 1996, La Bête humaine (translated by Roger Pearson), Oxford: Oxford University Press, ISBN 978-0-199-53866-9
• 2007, The Beast Within (translated by Roger Whitehouse), London: Penguin, ISBN 978-0-140-44963-1

• Die Bestie im Menschen, a 1920 German silent film, directed by Ludwig Wolff
• La Bête humaine, a 1938 movie directed by Jean Renoir
• Human Desire, 1954 movie based on the novel, and directed by Fritz Lang, starring Glenn Ford
• La Bestia humana, a 1957 Argentine movie, directed by Daniel Tinayre
• Cruel Train, a 1995 British TV movie, directed by Malcolm McKay
• La Bête Humaine, a 1993 BBC radio adaptation in three parts

Wikimedia Commons has media related to La Bête humaine.

• La Bête Humaine at Project Gutenberg (French)