"KL Gangster" tells the tale of two brothers who get involved in the world of gangsterism. The older brother Malek (Aaron Aziz) was imprisoned for five years after being betrayed by his own gang which was started by Shark (Syamsul), the step brother of the most influential gangster in Kuala Lumpur, King (Ridzuan Hashim). Malek who leads a normal life after being released, is pulled back into the world he left behind after all those years. Especially since his younger brother Jai (Adyputra) is influenced by the gangsters and decides to work for Shark bringing everything down in chaos.
Two brothers, Malek and Jai, are indirectly thrust headlong into the world of gangsters and crime when their father died 10 years ago. Since their father's death, Malek, Jai and their mother have been threatened by gangsters whom their father owes money to. Desperate, the wild Jai turns to crime, and will do anything as long as it pays well. Jai's behaviour sees vehement opposition from Malek and their mother, which breaks up their family. To make things worse, Malek finds out that his sister Shera has been raped and their mother has cancer...
Prohibition is ending so bootlegger Bugs Ahearn decides to crack California society. He leases a house from down-on-her-luck Ruth and hires her as social secretary. He rescues Polly Cass from a horsefall and goes home to meet her dad who sells him some phony stock certificates. When he learns about this he sends to Chicago for mob help.
Marc, a troubled teenager, is bored in his native, depressing city of Sete. One day, a simple phone call makes him aware of the existence of Stephanie, a sister he has never met. Armed with a pistol his mother found, he goes out to find her. He steals money from a perfume shop, and is then stopped by a policeman who wants to search him. In the car, Marc threatens the policeman with his gun, demanding that he helps him find his sister...
Jerry and his two pals, Russ and Syd, are just looking for some easy money to help them break out of their nowhere lives in their nowhere town. Despite a bungled jewelry store heist which exposes their incompetence as criminals, a fateful event (and an old black-and-white film) convinces them that they can pull off an armored-truck robbery. While they are busy plotting their caper, their dysfunctional families spin out of control, all around them.
After hiding his loot and getting thrown in jail, Ruby, a brooding outlaw encounters Quentin, a dim-witted and garrulous giant who befriends him. After Quentin botches a solo escape attempt, they make a break together. Unable to shake the clumsy Quentin Ruby is forced to take him along as he pursues his former partners in crime to avenge the death of the woman he loved and get to the money.
In the 1930s, the gangster pair Bonnie Parker and Clyde Barrow began robbing banks in U.S. cities until they were eventually killed in a police shoot-out.
A sophisticated con man mounts an intricate plan to rob an airport bank while the Soviet premier is due to arrive.