Set twenty-one years after I.D., Mo, Simon Rivers is a young Muslim police officer in the Metropolitan Police who is sent by Trevor Clymer, Richard Graham, to infiltrate the hooligan firm of Shadwell Town Football Club, who are reportedly fired up after the club’s takeover by a wealthy Russian oligarch. Mo tracks down Eddie, Perry Fenwick, who has moved on to a different life as a stand-up comedian performing in a pub run by Gerry Edwards, a former Shadwell player. Eddie warns Mo about the dangers of the Shadwell firm and urges him to be careful not to be drawn in, reminding him of the alcoholism, drug abuse, violence, and racism that accompany such an assignment.
Mo begins frequenting The Rock pub (now renamed La Chien), where he becomes acquainted with Shadwell’s rough-edged circle: Nick, Andy Rush; Danny Boy, Paul Popplewell; and Gumbo, Lee Ross. Danny initially clashes with Mo, becoming furious after losing a game of pool to him. After a tense moment, Mo leaves the pub and heads toward the stadium, where he encounters a group of Bolton Wanderers fans. Without drawing attention, Mo clumsily strikes a wall to feign injury and then returns to the pub. When Nick and Danny witness the ruse, Shadwell’s firm bursts out to ambush the Bolton fans, and Mo’s capable performance in the melee earns him a begrudging acceptance among the firm.
Mo is introduced to Vinnie, Linus Roache, one of the firm’s leaders. Mo tries to shadow Vinnie, but is caught. Vinnie takes him to his house, where his wife Alison, Christine Tremarco, prepares them dinner. Vinnie explains that he is also undercover and reveals his mission: he has been sent to infiltrate a faction of far-right extremists connected to the club who oppose Shadwell’s plans to build a new mosque next to the stadium. The firm then travels to Amsterdam for Shadwell’s Europa League first-leg clash with Tambuur SC. In a night of distraction, Andy, Danny Boy, and Gumbo engage in sex with prostitutes, and Mo joins them in consuming marijuana cakes, which leave them groggy and asleep in the pub, causing them to miss the game. When they wake, they realize they have let Vinnie down, and they return to London.
Back in the city, Mo goes to Vinnie’s house to warn Alison about Vinnie’s arrest; she allows Mo to sleep on the sofa. The next morning Vinnie returns, and Alison sends Mo out to hide in the shed, presuming Vinnie suspects infidelity. Vinnie arrives with Dave, Neil Pearson, George, Benjamin Harris, and Hunt, Duncan Airlie James, members of the English Defence League. A plan is unveiled to place a bomb inside a local mosque, with Hunt producing a homemade device that George realizes is about to detonate. Vinnie rushes out and hides the bomb in his shed, while Mo escapes. Hunt threatens Mo at gunpoint, but Vinnie declares his own Sikh identity and his hatred for extremism, while Dave offers Mo the option to join their group, which Mo accepts.
Shadwell makes it through Tambuur’s defence and advances to a tie against Athletic Bilbao. On the ferry to Bilbao, Danny Boy grows suspicious of Mo and accuses him of being a journalist, but the others dismiss the concern, and Danny ultimately accepts Mo’s sincerity. Gumbo confides in Mo that he knows Mo is a policeman, and Mo confesses as well; Gumbo swears he won’t tell anyone. The Bilbao leg fans meet them on the Spanish coast, and a confrontation erupts as they disembark.
Upon returning to London, Alison visits Mo at his boat house, and they share a moment of intimacy before Mo reiterates that he intends to continue with his assignment. Meanwhile, Dave meets with Kash, Shahid Ahmed, one of the Muslim leaders, and tells him that the mosque’s future depends on taking a hit to allow the construction of another mosque. The plan to detonate a bomb at the mosque on the night of Shadwell’s second-leg match against Bilbao hinges on Mo slipping the device inside in a hidden bag, with Gumbo’s help. As a precaution, Mo warns Gumbo and asks for his assistance, and Gumbo agrees. Mo then teams up with Vinnie, Hunt, George, and Dave to place the bag in Mo’s backpack and heads toward the mosque, with George following close behind to ensure a clean getaway.
At the mosque, Mo places the bomb and begins to leave, but he is confronted by George. Before George can shoot, Vinnie leaps in and shoots George, saving Mo. The bomb, however, has already been moved by Gumbo, who has taken the bag to The Kennel, where the match has concluded. The device detonates, killing Gumbo, who is later depicted on the news as a lone-wolf bomber driven by a desire to strike back at Shadwell’s Russian owner.
Mo joins Andy and Danny Boy to lay flowers outside the pub in Gumbo’s memory, then reconnects with Eddie at Gerry’s pub for a quiet tribute. In the closing scene, Mo returns to the mosque dressed in traditional Islamic clothing, signaling a complicated personal reconciliation with his faith and identity as he moves forward from the mission.
