Lenny Cole (Wilkinson) is a crime boss who calls the shots in London's underworld and real estate market. We learn all about Lenny from Archy (Strong)—his second in command—who serves as the film's narrator. When a wealthy Russian property dealer by the name of Uri Omovich (Roden) looks to Lenny for help on a major new deal, Lenny is eager to assist (for a very large fee, of course). Uri agrees to pay, and as a show of faith, he insists that Lenny borrow his "lucky" painting. Uri then asks his accountant, Stella (Newton), to transfer the money to Lenny, but things quickly go awry when a band of thieves known as the The Wild Bunch consisting of One Two (Butler) and Mumbles (Elba)—intercept the money before it reaches him (at the behest of Stella). To make matters worse, the lucky painting has mysteriously been stolen, and the number one suspect is Lenny's estranged stepson, crack-addicted rock star Johnny Quid, who is presumed dead. As Lenny desperately tries to locate the painting, Uri calls in sadistic henchmen to recover his money.
In an attempt to find Johnny, Lenny and Archy enlist his former record producers Mickey (Ludacris) and Roman (Piven) to track him down or else their concerts and clubs will be shut down. When One Two, Mumbles, and Bob try to steal the second load of Uri's money they are wounded and chased by Uri's persistent hired mercenaries who engage them in a shootout and a lengthy foot chase. They nevertheless deliver the money to Stella as they did before. By this time Uri has grown impatient and has Lenny viciously beaten, demanding that the painting be returned and the money delivered. Two item peddling junkies manage to steal the painting from Johnny and sell it to the Wild Bunch, which is given to One Two who gifts it to Stella after they have sex. Mickey and Roman find Johnny and call Archy to have him delivered. After capturing the three, Archy and Lenny's men go to apprehend One Two who is already in the hands of Uri's vengeful mercenaries. Archy and his men kill the mercenaries and kidnap One Two as well as Mumbles and Handsome Bob who arrived to deliver the name of the talked about police informant inside the London underworld.
Uri arrives at Stella's house to seal their arrangements while also asking her to marry him, as he has been smitten with her for a long time. Immediately after, Uri spots his lucky painting in Stella's living room. After being asked how long she's had it, Stella says she's had it for years, not knowing it's actually Uri's. Feeling betrayed and enraged, Uri orders his associate inside to kill Stella.
Meanwhile, Archy brings Johnny, the Wild Bunch, Mickey, and Roman to Lenny's warehouse where Johnny begins to verbally provoke Lenny. Lenny then shoots Johnny in the stomach before he finishes telling Archy that Lenny is the rat. Lenny then orders Johnny, Roman, and Mickey escorted downstairs while demanding that the Wild Bunch to tell him where the money is. Handsome Bob offers Archy the documents in his jacket pocket which reveals the informant, code named "Sidney Shaw," to be Lenny. Lenny had arranged with the police to give up many of his associates for prison at any given time in exchange for his freedom. One Two, Mumbles, and Archy himself are among the people Lenny has ratted out over the years. With this new information brought to light, Archy frees the Wild Bunch and kills Lenny.
In the meantime, Johnny informs Mickey and Roman how they will be executed prompting Lenny's men to act prematurely. Mickey and Roman intervene and kill the men and Johnny kills two more guards waiting outside the lift. The Wild Bunch save them from the last remaining henchman and they all escape.
Some time later, Archy picks up a rehabilitated but still eccentric Johnny Quid from the hospital. Archy offers Uri's lucky painting to Johnny as a peace offering and "welcome home present," which Johnny accepts. Archy reveals to Johnny that obtaining the painting "cost a very wealthy Russian an arm and a leg." The film closes with Johnny proclaiming that with his new freedom, he will do what he couldn't do before: "become a real RocknRolla".