Big Dave, editor of the Daily Print tabloid, is snubbed by cannabis baron Mickey Pearson at a party and hires private investigator Fletcher to investigate Pearson's links to Lord Charles Pressfield. Pressfield, a duke, has a heroin-addicted daughter named Laura. Fletcher offers to sell his findings (typed up as a screenplay entitled Bush) to Pearson's right-hand man, Raymond, for £20 million.

Born into poverty in the United States, Pearson won a Rhodes Scholarship to Oxford University, where he began selling marijuana to fellow students before dropping out and building his criminal empire by violence. He now plans to sell his business to American billionaire Matthew Berger for £400m so he can retire peacefully with his wife, Rosalind. Pearson shows Berger one of the labs where he grows his cannabis under the estates of aristocratic landlords, who need cash for the upkeep of their stately homes. Pearson is later approached by Dry Eye, an underboss for Chinese gangster Lord George. Dry Eye offers to buy out Pearson's business, but he refuses. Pearson's lab is then raided by amateur MMA fighters and aspiring YouTubers "The Toddlers" who overpower the lab's guards, steal a van-load of marijuana and upload a rap video of their caper online. The fighters' trainer, known only as Coach, orders them to delete the video and is horrified when he discovers that the cannabis belongs to Pearson.

Following the raid, Pearson begins transferring his cannabis plants out of the estates as a safety precaution, while having Raymond investigate how the Toddlers learned of the lab's location. Also, at the request of Pressfield, he agrees to bring Laura home. Raymond retrieves her from a council estate where she is living with several other addicts. However, in a brawl with her flatmates one of Raymond's men accidentally pushes Aslan, a young Russian man, off the balcony to his death. Although Laura is then returned to her parents, she later dies of a heroin overdose.

Coach visits Raymond, apologises for his students' actions, and offers his services as penance. Coach has captured Phuc, a henchman of Dry Eye's who had informed Coach's crew about the lab location, although Phuc gets fatally run over by a train in a botched escape attempt. Pearson threatens Lord George for going after his lab, and destroys one of his heroin labs in retaliation. George chastises Dry Eye for his insubordination in attacking Pearson and offering to buy him out; George nods to a henchman to execute Dry Eye, but the man executes George instead.

Unknown to Pearson, Dry Eye is in league with Berger, who had wanted Pearson's business disrupted to reduce the price. Dry Eye has taken Lord George's place and still hopes to take Pearson's empire for himself. Dry Eye tries to kidnap Rosalind, who kills Dry Eye's men before she runs out of bullets in her two-shot derringer. Raymond kills an assassin sent to kill Pearson; the two rush to Rosalind and Pearson fatally shoots Dry Eye as he is about to rape her. Fletcher ends his story and Raymond orders him to leave his house.