Nick Taylor's graduation day ends in heartbreak when his girlfriend Caitlin Hannah Tointon breaks up with him, and he humbles himself in front of everyone by begging for another chance. His friend Shane Simpson [Hammed Animashaun] convinces him to take a break from the drama and head to the Giant Music Festival to move on, since they’ve already bought their tickets.
On the train they meet Amy [Claudia O'Doherty], a chatty, exuberant Australian who has made the festival a yearly ritual for almost a decade. Shane is drawn to her while Nick keeps his distance, and their attempt to hide from the conductor by staging an on-train orgy ends with all three being ejected for traveling on child tickets. After arriving at the festival on foot, Nick and Shane search for a campsite while Amy heads to her usual spot. They encounter Caitlin again, along with her wealthy university friends who invite the two guys to crash in their luxurious tent. A man nicknamed Pirate [Kurt Yaeger], who has an amputated leg and a particular interest in Caitlin, also makes his presence felt, playfully (and provocatively) putting down Nick by insinuating that his name should be “Lick.”
The festival atmosphere swirls with music and chaos as the trio explores. Nick prefers to stay away from the densest crowds, while Caitlin loses her phone. Nick retrieves it, only to find himself confronted by Caitlin and Pirate entering a tent together; he hides as they begin to have sex. The next morning, Shane and Nick discover they’ve camped next to Amy and spend the day with her. Nick endures another embarrassing moment when a man mistakes him for Harry Potter and knocks him into the mud, prompting him to storm off to his tent.
Later, Shane and Amy stumble upon a Druid wedding in the woods. The groom, Brother David [Chris Geere], reveals he is Hammerhead’s manager and is “bound to” his new bride, which turns out to be a male goat, leading to a prolonged, transgressive spectacle in front of festivalgoers. Meanwhile, Nick meets a woman dressed as a Smurf—Smurf Girl [Emma Rigby]—who gives him half a MDMA tablet and shares a night of drug-fueled adventures in a stranger’s car.
When Nick wakes, Smurf Girl has left, and he discovers a nipple ring. The trio searches for her, visiting piercing parlors and learning that Nick has tattooed “My Name's Not Lick” on his buttock and left a prosthetic leg behind. They eventually find Smurf Girl again in a different setting, but she remembers little of him. A hen party of women dressed as Smurfs offers them Smurf Girl’s contact if they perform a strip tease; the boys comply, are arrested, and their wristbands are confiscated, making a return to the festival impossible.
Tensions rise as Shane misses Hammerhead’s set, and the friends are picked up by Shane’s stepfather Robin [Jemaine Clement], who collects them to take them home. At a petrol station, Nick apologizes to Shane and even steals Robin’s car, driving back toward the festival. They manage to rejoin Amy by climbing a fence back into the grounds, during which Nick injures his nipple on a wire. Pirate, now working security, tries to stop them, but Brother David vouches for the trio, and they slip back backstage.
Nick finds Hammerhead in the VIP bar, where Amy hands him one of her homemade Chaffney bars, and Nick’s wound begins to be tended. Smurf Girl appears again, but she has little memory of him. Hammerhead [Noel Fielding] endures an allergic reaction to shellfish, and Amy’s attempt to inject him with an EpiPen fails. Shane takes the stage in the Hammerhead mask, performing a song he wrote himself, and the crowd loves it. Pirate tries to cut the show short, but Nick intervenes as the moment builds. In a wild finale, Amy removes Pirate’s artificial leg and tosses it into the crowd. The crowd erupts, Nick and Amy reconcile, and Shane and Amy share a kiss on live camera. The pair stumble toward the pit, misjudge the jump, and tumble, only to be seen crowd-surfing away during the end credits.
The trio heads home by train, with Shane and Amy now a couple. Nick sits beside an elf-costumed girl, only to hide from the conductor once more as they attempt to return using child tickets.
