Plot

A group of juvenile delinquents live a violent and crime-filled life in the festering slums of Mexico City, as the morals of young Pedro are gradually corrupted and destroyed by the others.

Hell-bent on revenge, cocky reform-school runaway El Jaibo returns to his old neighborhood in post-World-War-II Mexico City's poor and squalid slums, to reunite with his faithful gang of juvenile delinquents and street urchins. However, as the dangerous ringleader lives and breathes retribution, his destructive obsession to find the informant who supposedly sent him to jail will intricately interweave his bitter fate with that of Pedro, his weak, unwitting accessory, in a despicable act of pure evil. In the end, are humans inherently good or bad? Is immorality contingent with society?—Nick Riganas

El Jaibo escapes juvenile jail and reunites with the street gang that he leads. El Jaibo's gang attempts to rob a blind street musician. They fail at first, but later track him down, beat him, and destroy his instruments.

With the help of Pedro, El Jaibo tracks down Julián, the youngster who supposedly sent him to jail. El Jaibo puts his arm in a fake sling and hides a rock in it. El Jaibo confronts Julián, who denies that he reported him to the police. Julián refuses to fight El Jaibo because it wouldn't be a fair fight with El Jaibo's arm broken. As Julián starts to walk away, El Jaibo hits him in the head with the rock. He then beats Julián to death and takes his money. El Jaibo warns Pedro not to report the crime, and since he shares Julián's money with Pedro, Pedro is an accomplice to the murder.

Pedro's mother resents her son's behavior, and shows signs that she doesn't even love him or care for him as a son. Pedro is extremely saddened by this and vows to start behaving better. He finds work as apprentice to a blacksmith. One day, El Jaibo comes to talk with him about their secret and, unbeknownst to Pedro, steals an expensive knife from the blacksmith's table. Pedro is accused of the crime and sent to a juvenile rehabilitation program, the "farm school," where he misbehaves and kills two chickens. The principal gives Pedro a test. He hands Pedro a 50 pesos bill to run errands with as a test of trust. If Pedro returns from the errands, he can be trusted. If he doesn't, the principal is out 50 pesos. Pedro accepts the offer and leaves with the intention to complete the errands. As soon as he leaves, he encounters El Jaibo, who steals the money. Upset that his attempt to be good was foiled again, Pedro tracks down El Jaibo and fights him. The fight ends in a stalemate, but Pedro announces to the crowd that it was El Jaibo who killed Julián. El Jaibo flees, but the blind man has heard the accusation and tells the police.

Pedro tracks El Jaibo down once again to murder him. El Jaibo kills Pedro. While fleeing, El Jaibo runs into the police. As El Jaibo tries to run away, the police shoot and kill him. Meche and her grandfather find Pedro's body in their shed. Not wanting to attract the police, they hide the body and take it to throw it away. On their way, they pass Pedro's mother, who, though once unconcerned with her disobedient child, is now searching for him. Meche and her grandfather dump his body down a garbage-covered cliff.