In the mid-1910s in rural England, Jemima and Jeremy, the two young children of widowed unsuccessful inventor Caractacus Potts, become enthralled by the wreck of a champion racecar. When they learn the car is due to be scrapped, they return home ("You Two") and beg their father to save it. To raise money, he attempts to sell one of his inventions, a musical hard candy, but the candy's whistle attracts a horde of dogs, ruining his sales pitch ("Toot Sweets").
That evening, Caractacus sings his children a lullaby ("Hushabye Mountain") before going to a carnival, where he attempts to raise money with another of his inventions, an automatic hair-cutting machine. It malfunctions, ruining the customer's hair, and, in order to escape the furious customer, Caractacus joins a spirited song-and-dance act ("Me Ol' Bamboo"). He earns enough money in tips to buy the car and rebuilds it, naming it "Chitty Chitty Bang Bang" after its unusual engine sounds. For their first trip in the car ("Chitty Chitty Bang Bang"), Caractacus and the children go to a beach to have a picnic. They are joined by Truly Scrumptious, the wealthy heiress to the candy company, and, though she and Caractacus have previously had heated encounters, everyone has a pleasant time ("Truly Scrumptious"). At the beach, Caractacus tells the children a story, beginning an extended fantasy sequence.
Caractacus' story
In the story, the nasty Baron Bomburst, tyrant of the fictional land of Vulgaria, attempts to steal Chitty. The family escape thanks to Chitty's miraculous transformation into a boat, and Truly goes home to Scrumptious Manor ("Lovely Lonely Man"). The Baron sends two bungling spies to get the car, but they fail repeatedly and eventually decide to kidnap Caractacus instead, but mistake Grandpa for Caractacus. As they fly away in their airship ("Posh!"), Chitty sprouts wings and propellers, and the family pursues the airship all the way to Vulgaria.
Grandpa is taken to Bomburst's castle, where the Baron has already imprisoned several other elderly inventors, and they are ordered to make another floating car, though their attempts fail ("The Roses of Success"). When the Potts party arrives, they find children have been outlawed in Vulgaria, as the Baron's wife, the Baroness, hates them. The kindly Toymaker harbours the Potts family and Truly in his toyshop. The group disguise themselves as jack-in-the-boxes to hide the children from the Child Catcher, but Chitty is discovered and taken to the castle. While Caractacus and the Toymaker search for Grandpa and Truly searches for food, the Child Catcher returns and traps the children. The Toymaker takes Caractacus and Truly to a grotto beneath the castle where the townspeople have been hiding their children ("Hushabye Mountain" (reprise)), and Caractacus concocts a scheme to free the people from the tyranny of the Bombursts.
The next day, which is the Baron's birthday ("Chu-Chi Face"), the Toymaker sneaks Caractacus and Truly into the castle disguised as dolls that sing and dance ("Doll on a Music Box/Truly Scrumptious (Reprise)"). At Caractacus' signal, the Vulgarian children swarm the banquet hall, overcome the Baron's guests, capture the Baron, Baroness, and Child Catcher. The Vulgarian adults storm the castle, while Caractacus, Truly, and the Toymaker free Jemima and Jeremy. After that, they join the fight against the Baron's soldiers. Chitty comes to save them and Grandpa is rescued. With the battle won, the Potts family and Truly bid farewell to Vulgaria and fly back to England.
After the story
As Caractacus' story concludes, an awkward moment ensues when the children ask Caractacus if the story ends with him and Truly getting married. Caractacus does not answer and tries to apologize for his children when he drops Truly off at her manor, saying that the difference in their social status would make a relationship between them ridiculous, offending Truly. Returning glumly to his cottage, Caractacus is surprised to find Lord Scrumptious waiting for him with an offer to buy his candy to sell as a dog treat. Overjoyed that he has finally made a successful invention, he rushes off to tell Truly, inadvertently causing her to crash into the pond once more. He rescues her and they admit their love for each other. Then, as they return home, Chitty flies up into the sky once again, this time without wings. ("Chitty Chitty Bang Bang" (Finale)).
Dick Van Dyke as Caractacus Potts
Sally Ann Howes as Truly Scrumptious
Lionel Jeffries as Grandpa 'Bungy' Potts
Gert Fröbe as Baron Bomburst
Anna Quayle as Baroness Bomburst
Benny Hill as Toymaker
James Robertson Justice as Lord Scrumptious
Robert Helpmann as Child Catcher
Heather Ripley as Jemima Potts
Adrian Hall as Jeremy Potts
Barbara Windsor as Blonde at the carnival
Davy Kaye as Admiral
Alexander Doré as First Spy
Bernard Spear as Second Spy
Stanley Unwin as Chancellor
Peter Arne as Captain of the Guard
Desmond Llewelyn as 'Bill' Coggins
Victor Maddern as Junkman
Arthur Mullard as Big Man (Cyril) at the carnival
George Leech as Chitty's original driver (uncredited)
Richard Wattis as Philips, the secretary at Scrumptious Sweet Co. (uncredited)
Michael Audreson as Peter, the blond Vulgarian boy (uncredited)
loosely based on the children's novel Chitty-Chitty-Bang-Bang: The Magical Car (1964) by Ian Fleming.
Van Dyke was cast in the film after he turned down the role of Fagin in the 1968 musical Oliver!. The role of Truly Scrumptious was originally intended to Julie Andrews to reunite her with Van Dyke after their success in Mary Poppins (1964), but Andrews rejected the part because she felt it was too similar to Poppins; Sally Ann Howes, who had replaced Andrews as Eliza Doolittle in My Fair Lady on Broadway in 1958, was then offered the role, and she accepted.