In London, the British mob boss Lenny Cole (Tom Wilkinson) rules the growing real estate business using a corrupt Councillor (Jimi Mistry) for the bureaucratic services and his henchman Archy (Mark Strong) for the dirty work. A billionaire Russian businessman, Uri Omovich (Karel Roden), plans a crooked land deal, and London's crooks all want a piece of it. Other key players include the underhand accountant Stella (Thandie Newton) and ambitious small-time crook One-Two (Gerard Butler) leading a group called the "Wild Bunch" which includes Mumbles (Idris Elba) and Handsome Bob (Tom Hardy).
Lenny charges Uri  7,000,000 for the crooked deal; Uri has his accountant Stella find funds. Uri lends his lucky painting to Lenny as a sign of friendship. Stella, however, double-crosses Uri and tips off the Wild Bunch to steal the money, while the painting is stolen from Lenny's wall by his junkie rocker stepson Johnny Quid (Toby Kebbell), who disappears. Lenny and Archy coerce his former managers Mickey (Chris "Ludacris" Bridges) and Roman (Jeremy Piven) into tracking down Johnny. Handsome Bob also gets close to a lawyer who has information on a prevalent undercover informer in their criminal circle.
After Uri's money is stolen by the Wild Bunch a second time, his assistant Victor begins to suspect that it is Lenny who has been stealing the money and purposely keeping Uri's painting from him to resell it. This theory enrages Uri, who lures Lenny to a private golf game in order to break his leg, warning him to return his painting without delay.
Cookie (Matt King) happens to buy the painting from some crackheads who had just stolen it from Johnny's hideout. Cookie then gives the painting to One-Two who, in turn, offers the painting to Stella (after a sexual encounter) as a token of appreciation. After Stella leaves his flat, One-Two is surprised by Uri's henchmen but is rescued, and then kidnapped, by Archy and his goons who had come looking for Uri's money.
Uri wants to marry Stella, whom he has long admired. At Stella's house he proposes, but he spots the painting. Stella lies and says she has had it for years. Uri, enraged by this and realizing that Stella betrayed him, orders Victor to kill her.
Archy brings Johnny, Roman, Mickey and the Wild Bunch to Lenny's warehouse where Lenny orders Johnny executed. He demands that the Wild Bunch tell him where the money is or else they will be killed "very slowly". Handsome Bob offers the legal documents concerning the informant in his pocket to Archy. Archy recognizes the pseudonym used on documents, "Sydney Shaw", as belonging to Lenny. Lenny arranged with the police to routinely lock up many criminal associates (including Archy himself) for years at a time in order to enhance his own standing in the criminal underworld and to ensure his own freedom. Archy orders Lenny's men to free the Wild Bunch and has Lenny drowned and fed to crayfish.
In the lift, Johnny graphically explains to Roman and Mickey that they will also be killed in order to leave no witnesses, and graphically explains the manner of their executions. His description unnerves the man who's to execute the three men, prompting him to act prematurely. Having also already anticipated this move, Johnny warns Mickey and Roman to intervene and kill their would-be executioner. Johnny shoots two more men waiting at the top of the lift and they escape the last of Archy's men (with the help of the Wild Bunch).
Later, Archy picks up Johnny from rehab. Archy gives Uri's lucky painting to Johnny as a peace offering. Archy says that obtaining the painting "cost a very wealthy Russian an arm and a leg" implying he had Uri killed. Johnny proclaims that, with his new-found freedom from addiction and his father, he will do what he could not before: "become a real RocknRolla".
Output: Why does Archy kill Lenny?