Kyle Alan "Nobby" Butcher, a devoted football hooligan and alcoholic, has been estranged from his younger brother, Sebastian Butcher, for a staggering 28 years. While Nobby has settled into a chaotic life in Grimsby with his partner Dawn and their eleven children, Sebastian has risen through the ranks to become one of MI6's most elite operatives under the name Sebastian Graves.
During a critical mission, Sebastian uncovers details concerning Rhonda George, a philanthropist hosting a benefit known as WorldCure—a potential target for assassination. Drawn by the news from his friends at the pub that Sebastian will be attending this event, Nobby makes the impulsive decision to go and seek out his long-lost brother. At the WorldCure gala, the drama escalates when Sebastian spots a hitman named Pavel Lukashenko, who is poised to take Rhonda's life using a weapon disguised as a video camera. Just as Sebastian readies himself to intervene, the unexpected happens: Nobby embraces Sebastian, causing an accidental shot that injures a young boy named Schlomo, played by Yusuf Hofri, and inadvertently leads to chaos as blood tragically infects Daniel Radcliffe with AIDS.
Faced with both law enforcement and dangerous criminals on their trail, the brothers find themselves in a precarious situation as they try to evade capture. Despite Sebastian's irritation, Nobby entices him to return to Grimsby for protection. Meanwhile, believing Sebastian has gone rogue, MI6 dispatches the assassin Chilcott to hunt him down. A frantic chase ensues in a pub, with both brothers narrowly escaping. However, Sebastian sustains injuries from lethal darts—Nobby, in a rather unsavory act, has to suck the poison from Sebastian's wounds to save his life.
As they navigate their way through this pandemonium, Sebastian gets intel from his handler Jodie, revealing that Lukashenko plans to strike a deal with Joris Smit at a remote South African lodge. The brothers head there, but things take a wild turn when Sebastian mistakenly injects himself with heroin that Nobby had bought, thinking it was a legitimate medication. In an unexpected twist, Nobby tries to assume Sebastian's identity during a mission, leading to comedic complications when he mistakenly flirts with a cleaner named Banu. Just as the misunderstanding escalates, Joris and his men interrupt, but Sebastian arrives right on cue to save Nobby.
Discovering that Lukashenko possesses a dangerous virus, they are confronted with another critical moment when Lina, Joris' wife, gets shot before she can divulge more. To escape their pursuers, the brothers engage in a ludicrous hide-and-seek inside an elephant's vagina, leading them to an even more ridiculous predicament involving elephant semen.
With a heartwarming yet humorous turn, Sebastian learns why Nobby felt compelled to leave him behind as a child. Nobby clarifies that their adoptive parents sought to adopt only one of them, and he selflessly dashed away to support Sebastian’s better future. The brothers find themselves making their way to Chile for a pivotal football cup final, only to realize a sinister plot is afoot involving the release of a virus into the stadium.
As their adventure intensifies, with Nobby defeating Lukashenko and saving Sebastian, they confront the ambitious Rhonda. In a sequence of chaotic events where Nobby’s children play their part to thwart Chilcott, the climax leads to the brothers boarding a firework rigged to explode the virus. In a chaotic finale, they land unconscious after the fireworks go off, creating hilarious consequences, one of which badly affects Donald Trump.
In the aftermath, the media reports that both brothers have perished saving the world while Jodie communicates to the brothers during their recovery that they were not affected by the virus, thanks to an unexpected antidote—elephant semen. Months later, Nobby and Sebastian are seen facing new adventures, already thrust back into action, when a deadly encounter with gunmen takes a humorous twist.
Lastly, in a post-credits scene filled with dark humor, the duo is seen in a car, leading to an unexpected and comical conclusion when Nobby decides that discretion is the better part of valour—by removing a witness.
Throughout this wild ride, the film navigates the bizarre dynamics of brotherhood, loyalty, and absurdity in a world threatened by chaos and misinformation.
