In 1967, Burt Munro, a legend in Invercargill, is celebrated for his charming and laid-back demeanor, not to mention being the proud owner of the fastest motorcycle in New Zealand and Australia. His fame has even landed him a feature in Popular Mechanics magazine. However, this acclaim is often overshadowed by the irritation of his next-door neighbors, who are increasingly frustrated with his unconventional habits. These include revving his bike early in the morning, relieving himself on his lemon tree, and letting his lawn grow wild. Nonetheless, Burt has one burning ambition: to travel to the United States and test the limits of his motorcycle at the famous Bonneville Speedway.
Unfortunately, while enhancing his beloved bike, Burt suffers a heart attack. Rushed to the hospital, he learns that he has angina and is advised to take it slow, avoiding his motorcycle. Dismissing the doctor's guidance, Burt continues to pursue his dream and begins taking medication to manage his condition.
Eventually, through sheer determination, Burt saves enough money to embark on a journey by cargo ship to Los Angeles, where he takes up the role of cook to cover his passage. Upon arrival, he faces a barrage of red tape, skepticism, and the general indifference often found in a bustling city. Yet, it is his straightforward yet friendly personality that helps him navigate these challenges. He wins over the friendly motel clerk, a transvestite named Tina, who assists him in clearing customs and helps him buy a car. A local car salesman even allows Burt to utilize his workshop and junkyard to craft a trailer, and later offers him a job after witnessing Burt's knack for fine-tuning cars. While flattered, Burt chooses to decline the offer in pursuit of his ultimate goal.
Burt's journey across America introduces him to countless kind-hearted individuals. He meets highway police who extend their support, a Native American man named Jake who lends a hand when his trailer breaks down, and a woman named Ada, who not only provides a garage for trailer repairs but briefly becomes his lover. He also forms a friendship with an Air Force pilot on leave from Vietnam.
Upon reaching the Bonneville Salt Flats, Burt encounters an unexpected roadblock: race officials refuse him entry due to his motorcycle lacking proper registration and safety gear. Fortunately, a spirit of camaraderie shines through as fellow competitors and spirited fans rally to assist Burt, ultimately allowing him to make a trial run. Despite facing several obstacles during his attempt, Burt's perseverance pays off as he sets a new land speed record reaching an impressive 201.851 mph (or 324.847 km/h) at the eighth mile of his run. The adrenaline rush culminates in a dramatic moment when he suffers burns on his leg from the motorcycle's exhaust, and after a thrilling fall, he skids to a halt. Against all odds, he returns to New Zealand celebrated as a hero.
In the epilogue, we learn that Burt took part in the Bonneville races an incredible nine more times, continuously battling to push and break new records, solidifying his place in racing history.
