Jack Hopkins is an aircraft designer and hands-on engineer with a passion for traction engines, owning one called The Iron Maiden. His boss, Sir Giles Thompson, is eager to sell a new supersonic jet aircraft he designed to American airline owner Paul Fisher, who has arrived in England with his wife Miriam Fisher and daughter Kathy Fisher.
The first encounter between Fisher and Jack goes badly, when the traction engine crashes into the front of Fisher's car on a narrow lane. They meet again at the airfield where the aircraft is shown to Paul Fisher and they recognize each other. Fisher, who has formed a wary opinion of Jack (without knowing he is the designer), states that he will not purchase the aircraft unless he likes the designer. Later Jack goes to the Fisher residence to discuss the aircraft with him, but the tension remains high as assumptions and pride mingle with professional ambition.
Fisher asks Jack to take Kathy to see some friends (her hire car broke down before she reached England) while he surveys a rival aircraft built by the opposition led by Lord Upshott. His son Humphrey Gore-Brown offers to drive them, and on the way they stop to visit a Duchess whose traction engine powers a Ferris wheel. The wheel is broken, and while Jack works on the engine, Kathy sits in a chair and is hoisted upward as it turns. A sudden downpour traps her in mid-air, and Fisher climbs to rescue her, while Jack remains temporarily stranded at the top. The machine falters and cannot be restarted; Kathy ends up taking Jack’s car, only to leave it abandoned in the countryside. Jack tracks her down to her friends and learns where his vehicle lies.
At Ascot Racecourse, Sir Giles invites the Fishers to see the competition, but they encounter another broken traction engine—this one named Princess Caroline. Jack makes a concerted effort to fix it, and the scene intensifies as tar stains the faces of Sir Giles and Kathy, and even stains Mrs. Fisher inside their Rolls-Royce. The arrival of Lord Upshott shifts the momentum, and he escorts the Fishers to Ascot. Believing he has lost the sale, Sir Giles sacks Jack, though the decision also leads to his own resignation.
Kathy then visits Jack at the home of his friend, fireman Fred Trotter. The traction engine sits out front that day as Kathy attempts to drive it away from an oncoming car. The engine lurches forward, knocking over a police officer’s pushbike and crashing into a barn. Jack comes to her aid, and in the chaos The Iron Maiden sustains damage to its safety valve, making it impossible to drive solo until it’s repaired.
With the rally season approaching, Jack is desperate to enter the annual Woburn Abbey steam rally with the machine. He and Fred head to Fred’s home for supplies, but Fisher arrives to demand answers about Kathy’s earlier actions. Fred ends up breaking his leg by an accident with his son’s roller skate, which prevents him from participating that day. In a chaotic turn, Fred unintentionally helps by causing Fisher’s car to slide into a ditch. Jack gives Fisher a lift when his own car cannot free itself, and this moment of shared commitment helps swing Fisher toward backing Jack’s cause. The two men form a genuine alliance, with Fisher recalling fondly that he had been “stoking boilers when Jack was in short pants,” a wink at the old-school camaraderie behind their shared vocation.
Their journey to Woburn Abbey is long and eventful, forcing them to camp beside the engine at night and to improvise fuel as they go. They cross paths with Admiral Admiral Sir Digby Trevelyan and his “England Expects” engine, who has laid a trap—a hidden pit designed to stop rivals. Undeterred, they dig themselves out and even raid the Admiral’s supply signs for fuel, burning bags, and in a pinch even their own footwear and clothing to keep the Iron Maiden running. The daring and improvisation are a testament to their grit and to the unlikely bond forming between the two men.
When they finally reach Woburn Abbey, the rally features nearly a hundred traction engines of the era, a showcase of power and tradition. The Iron Maiden arrives just in time, and Fisher’s back injury during a coal retrieval forces him to withdraw from the main rally. Mrs. Fisher and Kathy witness Fisher’s awkward moment as he runs in his underwear with the coal—a comic but telling image of the day’s chaos. With Fisher sidelined, Kathy makes a bold choice to join Jack on the engine.
From last place to first, they pilot The Iron Maiden through the field, driven by teamwork, trust, and a shared dream. The finish line brings a kiss between Jack and Kathy, a moment of triumph that is tempered by tragedy as the engine boils over and explodes in a dramatic finale. In a final flourish, the beloved machine is memorialized when Jack’s new jet is named after it, sealing a new era that fuses traditional steam power with modern aviation ambition.
