Kyle Alan "Nobby" Butcher, [Sacha Baron Cohen], has spent 28 years apart from his younger brother Sebastian Butcher, who is now known as Sebastian Graves, [Mark Strong], one of MI6’s most capable operatives. After an initial interrogation, Sebastian uncovers details about a philanthropic magnate, Rhonda George, [Penélope Cruz], who is hosting a high-profile event called WorldCure and may become a target for assassination. Assigned to the case, he heads to the event, while Nobby’s pub crew hears that his brother will be there and pushes him to reconnect with the missing kin. The WorldCure gala becomes the setting for a dangerous confrontation when Pavel Lukashenko, [Scott Adkins], a ruthless hitman, arrives with a plan to kill Rhonda. Lukashenko’s weapon is a gun disguised as a video camera, and as he readies his shot, a stunned Nobby tackles him and inadvertently disrupts the operation.
The ensuing chaos leads to a shocking tragedy: the spray of blood strikes an AIDS-infected boy, Schlomo, [Yusuf Hofri], in the mouth, changing the course of the night in a staggering, darkly comic twist. The brothers are forced to flee as authorities close in, with both men hunted by criminals and law enforcement. To survive, they seek refuge in Grimsby, despite Sebastian’s protests, a decision that pulls them into a web of dangerous loyalties and buried family history. MI6, convinced that Sebastian has gone rogue, dispatches an assassin named Chilcott, [Sam Hazeldine], to eliminate them. The chase leads to a pub where the two brothers narrowly escape, but Sebastian is injured by two Lonomia toxin darts that threaten his life.
Nobby takes on a desperate, improvised rescue: he sucks the poison from Sebastian’s wound, a moment that hardens their bond and compels them to keep moving. The trail leads to a South African lodge where Lukashenko intends to seal a deal with Joris Smit, [Nick Boraine], drawing the brothers deeper into a perilous international plot. To infiltrate Lukashenko’s operation, Nobby impersonates his brother, while Sebastian, compelled by duty, makes a dangerous entrance to support the ruse. They learn that Lina, who wears a similar guise to Joris’ spouse, holds vital information, but she is fatally shot by Chilcott’s men before she can reveal more. In a bizarre escape sequence, the brothers hide inside an elephant’s vagina to avoid pursuit, emerging smeared with elephant semen but alive.
Back on track, they confront the past: Nobby reveals the true reason he left Sebastian years earlier—his adoptive parents could not decide which brother to keep, so he ran away to give Sebastian a chance at a better life. The siblings reconcile and press onward toward a final confrontation in Chile, where England faces Germany in a football final and the WorldCure conspiracy aims to unleash its virus on the arena. Rhonda, the mastermind, visits Sebastian and unveils her plan to release the virus through fireworks. Nobby fights his way through Lukashenko’s cadre to reach Rhonda, while Sebastian is held by the terrorists. The brothers’ kids play a pivotal role in fending off Chilcott’s pursuit: they hurl Schlomo’s wheelchair, knocking him down and derailing the assassin’s advance. Nobby’s gun jams at a crucial moment, forcing him to improvise as the fireworks ignite.
With seconds to spare, the brothers sit atop the fireworks that carry WorldCure, and Sebastian chooses to share the burden at Nobby’s side. The pair are knocked unconscious when the devices explode, but the virus plot is neutralized by an unlikely antidote—elephant semen—revealing a bizarre, comic, and hopeful reversal. The news announces Rhonda’s arrest and declares that the Grimsby brothers have died heroically, saving countless lives; in truth, they survive and recover in a hospital, receiving new identities from Jodie, [Isla Fisher], who assures them they can start fresh. Eight weeks later, Nobby and Sebastian are on a covert mission in Indonesia, where a routine contact turns perilous when gunmen unexpectedly reveal themselves to be part of Nobby’s own team, leaving the brothers to confront a final, unsettling twist.
In a post-credits moment, the brothers are cruising in a car when a routine street encounter becomes a grim reminder of the price of their double lives: Nobby shoots a man to “leave no witnesses,” a closing jolt of violence that lingers with the brothers’ uneasy, unspoken bond. The WorldCure crisis is resolved in a way that preserves life, but the brothers’ future remains shadowed by danger, loyalty, and the fragile peace of a family forged through improbable, chaotic odds.
