Reggie enters into a relationship with Frances, the sister of his driver, and they ultimately marry; however, he is imprisoned for a previous criminal conviction, which he cannot evade. While Reggie is in prison, Ron's mental problems and violence lead to severe setbacks at the nightclub. The club is almost forced to close after Ron scares away most of the customers. When Reggie is finally released from prison, the two brothers have an all-out fist fight on the first night after Reggie's release, but they manage to partially patch things up.
The brothers are approached by Angelo Bruno of the Philadelphia crime family on behalf of Meyer Lansky and the American Mafia, to try to interest them in a crime syndicate deal. Bruno agrees to a fifty-fifty deal with Reggie to split London's underground gambling profits in exchange for local protection from the Kray brothers. Initially, this system is highly lucrative for the Kray brothers. However, the results of Ron's barely concealed violence continue to cause problems with Scotland Yard, who open a full investigation of the Kray brothers.
Reggie beats and rapes Frances and she leaves him. Reggie then approaches her to start afresh offering her a holiday to Ibiza. However, she is soon found dead after committing suicide with an overdose of prescription drugs. The brothers' criminal activities continue, and they are unable to thwart the escalating Scotland Yard investigation by Detective Superintendent Leonard "Nipper" Read, who soon arrests Ron. The final scene shows a police squad breaking down the door to Reggie's flat in order to apprehend him.
The closing captions indicate both brothers receiving criminal convictions for murder. They died five years apart, Ron from a heart attack in 1995, and Reggie from cancer in 2000.
In the 1960s, Reggie Kray is a former boxer who has become an important part of the criminal underground in London. At the start of the film, his twin brother Ron is locked up in a psychiatric hospital for insanity and paranoid schizophrenia. Reggie uses threats to obtain the premature release of his brother, who is rapidly discharged from hospital. The two brothers unite their efforts to control a large part of London's criminal underworld. One of their first efforts is to muscle-in on the control of a local night club, using extortion and brutal violence.