Matt Buckner, portrayed by Elijah Wood, faces a life-altering turn of events when he is expelled from Harvard University after trace amounts of cocaine are found in his dorm room. Unbeknownst to many, the cocaine actually belonged to his roommate, Jeremy Van Holden (a character played by Terence Jay), a member of a well-off family that wields considerable influence. Feared and pressured, Matt takes the blame in exchange for a hefty sum of $10,000 from Jeremy. Seeking a fresh start, he relocates to the United Kingdom to stay with his sister, Claire Forlani, her husband Steve Dunham (Marc Warren), and their young son, Ben (James Allison).
Upon arriving in the UK, Matt quickly crosses paths with Steve's brother, Pete, a boisterous and intimidating Cockney who runs a local football hooligan firm—an organised group of football supporters known for their violent clashes following matches. Despite his initial resistance to introducing an American to his world, Pete reluctantly agrees to take Matt to a football match between West Ham United and Birmingham City, buoyed by the promise of financial motivation from Steve. Their burgeoning friendship takes a turn when, after defeating Matt in a playful tussle, Pete decides that Matt may pick up some valuable lessons from the experience.
At the local pub, the Abbey, Matt meets Pete's entourage, and they welcome him into their fold—except for the ever-skeptical Bovver (Leo Gregory). Following some drinks, the excitement of the match gets overshadowed by a desire for confrontation. When Matt opts out of the post-match fight with the Birmingham fans, he soon finds himself in a perilous situation being attacked by three of them. However, much to his astonishment, he is saved by members of the GSE, who stand their ground against overwhelming odds until they are able to drive the Birmingham thugs away. This pivotal moment marks Matt's initiation into the firm.
As time progresses, Matt’s growing involvement in the gang leads to a confrontation about his past. After an argument with Steve, he decides to move in with Pete, and their camaraderie deepens as they share stories of their lives. However, as the GSE prepares for an away game against Manchester United, the stakes rise dramatically. Initially not invited, Matt sneaks aboard the train, where they learn that a rival firm awaits them at the station. In a clever ploy, Matt persuades the van driver to allow them through the rival’s ranks under the guise of transporting equipment for a film. The ensuing chaos results in an unexpected victory for the GSE, solidifying Matt's place among them as they chant, "There's your famous GSE."
Tensions rise as jealousy and old wounds resurface within the firm when it is revealed that their arch-rivals, the Millwall firm led by Tommy Hatcher (Geoff Bell), are out for blood. The firm’s rivalry takes a more sinister turn when it’s uncovered that Steve had a past as “The Major” of the GSE and was involved in a tragic incident years prior which ended in the death of Tommy’s son. As heat escalates, Bovver’s betrayal ignites a series of events leading to the Millwall firm launching a violent attack on the Abbey, leaving a trail of destruction in their wake. In a heartbreaking moment, Steve becomes the target of Tommy’s wrath and suffers a severe injury, provoking unexpected loyalty from Bovver who assists him despite their earlier fallout.
The film reaches a climax near the iconic Millennium Dome where the GSE firms clash in an explosive melee. Matt, alongside Bovver, charges into battle only to find his family caught in the crossfire when Shannon and Ben are attacked. Pete’s ultimate sacrifice appears when he confronts Tommy Hatcher, igniting a chaos that results in Pete’s tragic death, capturing the immediate aftermath of raw emotions from both sides. In this chaotic atmosphere, Matt understands the weight of the past decisions as he is painfully reminded of the futility of their violent existence.
Returning to the United States, Matt finally confronts Jeremy in a restroom, bearing the burden of their shared history and the impact of choices made. Armed with a tape recorder that captures their incriminating conversation about the cocaine scandal, Matt is ready to thwart Jeremy’s arrogance. With a calm demeanor amidst the confrontation, he walks away with newfound resolve as Jeremy collapses amid his defeat. The film concludes on a note of bittersweet triumph as Matt walks away, humming "I'm Forever Blowing Bubbles," representing the fractured yet hopeful journey he has traveled.
