The Iron Maiden

Jack Hopkins, a hands-on aircraft designer, and his boss Sir Giles Thompson aim to sell a new supersonic jet to Paul Fisher. Their first encounter with Fisher is rocky, as the Iron Maiden crashes into Fisher's car on a narrow lane, souring the initial impression. The incident establishes a tense, competitive dynamic between the parties.

The Fishers meet Jack again at the airfield; they recognize each other despite not knowing their connection, and Fisher, unaware that Jack is the designer, grows to dislike him. He declares he will not purchase the jet unless he likes the designer.

Jack visits the Fishers at their hotel and discusses the aircraft and the potential sale. They debate the jet's prospects, the terms of a possible deal, and the obstacles they must overcome.

Fisher asks Jack to take Kathy to see some friends, and they stop to view a Duchess's traction engine powering a Ferris wheel. Kathy climbs into a chair as the wheel rises, but rain disrupts the rescue and the ride stalls. Kathy ends up taking Jack's car and drives off, and Jack later tracks down where his own car was left.

At Ascot Racecourse, they come across a broken-down traction engine named 'Princess Caroline' and Jack tries to fix it while Lord Upshott arrives to present the rival engine. Sir Giles believes the sale is slipping away and sacks Jack, and he resigns in protest.

Kathy visits Jack at Fred Trotter's house and tries to drive The Iron Maiden. It crashes into a barn and Jack has to intervene to keep her safe. The crash damages the safety valve, making the traction engine impossible to drive solo.

Fisher confronts Jack at Fred's house about Kathy's actions. Fred breaks his leg by falling over his son's roller skate, preventing participation in the journey. Later, Fred's mishap leads to an accidental run-over of the policeman's pushbike, sending Fisher's car into a ditch. Jack pulls Fisher out and gives him a lift, and the two begin to bond as allies for the journey to Woburn.

With their alliance formed, they head for Woburn Abbey to enter the rally. The journey is long and they stop to camp beside the Iron Maiden, cooking breakfast on a shovel. They forget a bag of coal at the campsite, adding to their hardships.

They take a shortcut through Admiral Sir Digby Trevelyan's land and trigger a hidden pit, leaving the Iron Maiden stuck. After digging out, they salvage wooden 'no trespassing' signs to use as fuel. With fuel running low, they burn bags, footwear, and clothing, ending up in their underclothes.

They finally reach Woburn Abbey and enter the rally, joining almost 100 engines. The Iron Maiden arrives just in time, but Fisher injures his back while collecting coal and withdraws from the rally. Mrs Fisher and Kathy arrive with Lord Upshott and the Duke of Bedford to witness the moment.

With Kathy's bold decision to join Jack on the engine, they drive The Iron Maiden from last to first and win the rally. At the finish line they embrace and share a kiss as the engine boils over and explodes. The Iron Maiden is memorialised when Jack names his new jet after it.