Short summary - The Beast Within or The Beast in Man - La Bête humaine
Micro-narration: The idyll of the Roubaud family collapses when the husband learns that his career owes to the fact that his wife was the target of harassment by Judge Granmoren. The assistant to the head of the Le Havre station has a plan to eliminate the seducer, which he practically immediately implements - he sticks a knife into the throat of the rapist when he returns to his estate from Paris on the train. There are almost no witnesses of the crime on the night express, but by the will of the circumstances, the machinist Jacques Lantier, who is visiting his aunt, sees the scene of the murder in the window of a moving train. He himself dreams of violence, and the bloody scene delights him. However, Jacques fails to consider the killer.
The locomotive driver Jacques Lantier feels the urge to kill a woman. He is afraid of this and leads a secluded life. He later discovers that he is in love with his locomotive.
The head of the Roubaud railway station learns that his wife Severina had a childhood relationship with Granmorin, the president of the railway community. Thanks to this, he and his wife receive all kinds of protection. On the train from Paris to Le Havre, they kill Granmorin and discard his body. Having committed a crime, they move to another carriage.
Jacques, meanwhile, visits his cousin Flora, who lives with her father, a switchman. He has a desire to kill her, but he confronts him and leaves. Accidentally, Jacques witnesses the murder of Granmorein and finds his body on the train tracks.
There is a suspicion that the murder was for the purpose of robbery. Roubaud and Severina are interrogated by the police, but find out that they had no motive to kill. Jacques points to Roubaud as a murderer. The judge concludes that the crime was committed by an eccentric Kabush who lives nearby, but this remains unproven.
The relationship between Roubaud and Severina is on the verge of breaking. They hide Granmorin's money and watch behind a closet. Roubaud begins to drink, and Severina and Jacques become lovers. At first, they think that Roubaud knows everything, but then their fears disappear.
Severina informs Jacques that her husband forced her to participate in the murder of Granmoren. In Jacques, the desire to kill a woman awakens again. He leaves his apartment in search of a new victim. But he does not commit murder. Later it turns out that he lost his desire to kill. Jacques believes that his love for Severine healed him.
Severina and Roubaud's relationship falls apart when she realizes that her husband alone spent the loot. Jacques manages to invest in his friend's shop. Severina invites Jacques to pocket the rest of her money. Roubaud is the only obstacle on her path to happiness. She invites Jacques to kill him. He watches over Roubaud, but his nerves fail, and he retreats.
Jacques' cousin, Flora, who is in love with him, learns that he and Severina are in a relationship and decides to kill both of them out of jealousy. She arranges a train crash that kills many people. Flora then throws herself under the train. Jacques, who was wounded during the disaster, is nursed by Severin.
Severeina falls into a trap set by Roubaud. Jacques must kill her husband. But he again finds the desire to kill the woman. He stabs Severina and flees. Kabush finds her body. Police believe that Kabush killed the woman on the orders of Rabu. Both are arrested.
Jacques returns and becomes a machinist again. But now he drives a different locomotive. He starts courting another girl. The novel ends on a scene when Jacques is driving a train in which soldiers travel to the German-French front. He has a conflict with the fireman, a fight breaks out, and both fall off the train, which rushes into the night, full of patriotic soldiers.