Luke, James Rolleston, is chased by several people in a car dump yard in Kaikohe. He dives into a working yellow Mini Cooper S and tears away, its engine roaring as the pursuit fades into the distance. Meanwhile Jon, Dean O'Gorman, an Auckland-based writer who cannot finish his book, decides to attend a wedding in Wellington that Suzie, Antonia Prebble, his ex-fiancée, is invited to. He borrows his friend's expensive suit and heads south. In Pōkeno, his car breaks down and catches fire, forcing Jon to continue on foot. He is almost run over by Luke on a rural road, and Luke agrees to give him a lift. In Waikato, the two inadvertently roll away from a petrol station without paying, drawing the attention of the police. Luke’s remarkable driving skills help them slip away, weaving through the countryside toward a drive-through burger joint where Keira, Ashleigh Cummings, an employee weary of rude customers, hops in on a whim. Keira is a vegan activist who wants to reach Wellington to participate in a protest against live export and a pre-event rave.
Jon arrives at the wedding and bitterly confronts Suzie; champagne spills over him as she brushes off the tension with a shrug. He discovers that his laptop containing the book draft has been ruined, and he ends up taking drugs provided by Keira’s friends, falling asleep in the coffin attached to the Mini used for the protest. By morning, police are on their trail again, and Luke’s driving prowess helps them escape by plunging into an open freight train car. Noah, Matt Whelan, calls Jon to reveal that the man at the wedding is Suzie’s gay friend.
On the train, the travelers shed their ordinary clothes and don old outfits, even the titular pork pie hat. Keira and Luke begin a romance and share a night together. Jon decides to head to Suzie’s house in Invercargill to talk things through, while Keira records a video stating that they are animal-rights activists heading to Invercargill. In Southland, Jon buys snacks at a dairy and learns their “gang” has become national news thanks to Keira’s posts. A dairy worker points to a TV report, and Jon bolts. Keira uploads another video from detention claiming the gang is unarmed, which only adds to the mounting pressure.
Luke makes a risky stop at another dairy and is shot by an aggressive police officer, sending him to hospital. Jon continues his journey alone and phones Suzie, who agrees to give him one last chance—he must show up at a cafe in Invercargill at 7 pm. The Southland Mini Club members rally around Jon, helping him shake off most of the pursuing cars, though one officer shoots his tyres, leaving the car to catch fire from friction. Jon finally reaches Invercargill almost too late and spots Suzie walking away from the cafe; he is arrested, but Suzie decides to become his lawyer.
In a mid-credits tease, Suzie and Jon decide to marry again, with Suzie waiting at the altar for hours. Meanwhile, Keira steals Luke—the wheelchair-bound one—from a hospital, and the pair vanish together, slipping away from the roving police presence.
