Alfie Wickers, Tom Davis leads Class K on a school trip to Amsterdam, only to have his day derailed when Mitchell, Mathew Horne, spikes Alfie’s crepe with magic mushrooms, sending Alfie into a vivid, unruly hallucination inside the Anne Frank Museum. He fixes his attention on Jing Hua, Kae Alexander, whom he mistakes for a panda, and becomes convinced that the life-size Anne Frank dummy is alive, culminating in a chaotic moment where Alfie steals the dummy in a cheeky parody of E.T. and tumbles into a canal. A cut scene inside the museum even shows Anne Frank pointing at Alfie and saying > "home".
One year later, Alfie schemes to take his class to Las Vegas, a plan that triggers the parent–teacher association into a furious protest. Deputy Head and Alfie’s father Martin Wickers, headmaster Shaquille Fraser, and teacher Rosie Gulliver rally to give Alfie another chance, arranging a surprise visit to his classroom to prove he can still teach. Meanwhile, Mitchell tries to tattoo “Class K Forever” on Alfie’s back, though Alfie faints before the ink can complete the message.
To placate the parents, Alfie fabricates a Cornwall itinerary and spins a tale that his best friend from school, Atticus Hoye, is hosting a house party in Cornwall. Susan Poulter, Joanna Scanlan, one of the most vigilant parents, accompanies the group and helps carry out the ruse, beginning with a pretend stop at the Eden Project. At the park, Alfie is forced to zip-wire across the entire site with his trousers around his ankles, while Mitchell smuggles a plant described as “nature’s laxative” to sabotage Susan’s drinks, igniting a cascade of mischievous mishaps.
The journey continues to Penleven Castle, where they glimpse John the Baptist’s foreskin, and Susan, overwhelmed, heads to the toilet, leaving the group unattended. Mitchell makes a last-ditch attempt to steal the foreskin but fails; Alfie retrieves it and, to cover their tracks, swallows the item. The troupe then arrives in Port Jago, slipping away to a local pub where the barman and Pasco Trevelyan, Iain Glen, discuss the Cornish Liberation Army (CLA), a cause Pasco quietly supports. Alfie and the others are mistaken for CLA members because of the unfinished tattoo on Alfie’s back, and Pasco recruits Alfie into the rebellion while Alfie learns that Atticus Hoye is hosting a party at a nearby house.
Susan, following behind, records events from a window, but Pasco slips her sleeping pills and stuffs her into a trunk before abandoning it in Cherbourg, France. Pasco then drags the group to a strip club, tasking Alfie with delivering cannabis to Atticus Hoye’s party the next night—unbeknownst to Alfie, the truck is packed with explosives. Meanwhile, Susan makes it back to the UK with some illegal immigrants.
Back home, the other teachers lose contact with the Cornwall trip as Alfie and the children arrive at Atticus’s party. Alfie endures bullying from his so-called friends and is forced to teabag a swan, an act that pushes him toward a breaking point. Feeling betrayed by nearly everyone, he phones Pasco to arrange a pickup, and Pasco uses the moment to detonate the truck, blowing up the grounds of the Hoye residence. Pasco drives the children toward Port Jago and proclaims Alfie as the leader of the Cornish rebellion, joined by many locals who reveal themselves as CLA members. The police, overwhelmed by the chaos and the media narrative about potential radicalization, enlist Interpol, who join Susan and the parents in the search effort.
Pasco explains that the CLA intends to seize Cornwall’s means of production, with the Eden Project as a likely target, but Alfie sabotages the plan while still feeling sympathy for Pasco’s cause. The situation escalates into a seizure of control, and Pasco imprisons the children, but Joe Poulter, Ethan Lawrence, discovers a secret passage from Penleven Castle to the beach, allowing the kids to escape. Rosie Gulliver, Sarah Solemani, and Fraser arrive by helicopter to rescue Alfie, and Pasco is arrested.
Six weeks later, Michael Hoye resigns as Port Jago’s MP. On results day, Mitchell again injects magic mushrooms into Alfie’s brownies, sending Alfie into another wave of hallucinatory confusion, ending with a peculiar, artful “Leavers Photograph.”
