In London, a refined gent in a bowler hat strolls the streets with flowers and chocolates, seemingly bound for a date. He pauses at a jeweller’s window, admires the rings, and then, in a sudden twist, tosses the box (containing a brick) through the glass and makes off with the jewels. A Citroën DS roars up, and he slides inside to join two accomplices. The police pursue, but the chase stalls at a junction when a fire engine needs to pass, and the trio is caught and sent to Wormwood Scrubs.
Upon release, they reason that a fire engine is the least likely mode of transport to be slowed by traffic. Their next move is to a fire engine salesroom, where a salesman extols the virtues of different machines. Strapped for cash, they cannot afford a £5000 new engine, so they head to a scrap yard to buy an old one instead. The plan shifts to stealing a well-kept 1930s fire engine stored at a remote station, swapping it with their scrap engine of the same type, and then burning down the old station to hide the theft, leaving the scorched scrap heap behind.
They park the newly acquired engine in a large shed in Smithfield and identify a jeweller near Berkeley Square as a target. They acquire firemen’s uniforms from a costume shop to complete the disguise. Their first attempt to pull off the jeweller’s robbery in this new setup ends in disaster. While one of them, Harry, dodges the police, he ends up taking refuge in a wedding-dress display and encounters Chantal, the French owner of the dress shop, whom he pretends is the daughter of a wealthy client. He arranges a dinner date with her. Meanwhile, Bernard and Alfie, still in the fire engine, are misdirected by a desperate homeowner who mistakes them for the real fire brigade as they try to pump out a flooded basement. Their intervention only makes the water worse, and they flee when the real fire brigade arrives, hoses trailing behind them.
The bungling continues to sharpen their resolve; they decide they need to be more professional so they can convincingly pass as trained firemen. An acquaintance, a mad professor known as “Arson Eddie,” is reluctant to help because his fixation is arson rather than prevention, though he knows a great deal about starting fires. A chance overheard outside a fire station leads them to Withers, a fire chief dismissed for arson, theft, and conduct unbecoming. He agrees to train them in exchange for a share of the bank job’s proceeds.
Chantal’s salon sits next to a bank, which gives them the idea to stage a fire in her basement as a way to get close to the vault. Madame Colette, Chantal’s business partner, reveals that the dress collection is insured for £20,000, underscoring the value at stake. Arson Eddie visits the dress shop posing as a potential client, “Mr Mountbatten,” and becomes both enchanted by the women and obstructed by repeated attempts to start a fire. Colette herself triggers a showroom fire by burning the curtains, advancing the duo’s plan.
The bank robbery unfolds from the basement while a real fire rages above, drawing in the real fire brigade. The thieves escape with a fire hose stuffed with banknotes, and Colette and Chantal are shocked to spot Harry and his “Mr Mountbatten” disguise on the fire engine. A policeman overhears the commotion and gives chase.
As they escape, two young girls with a burning treehouse flag them down again to join in tackling a fresh blaze. The trio remains determined, well equipped, and, above all, confident in their plan, but Alfie attaches the wrong hose to the pump and ends up spraying the banknotes instead of water, coating the scene in money.
The film closes with the crooks riding in the Black Maria, bound for another spell behind bars. Through the window behind the van, a royal limousine carrying the Queen is visible, and Bernard suggests he has yet another idea for the perfect getaway.
