This version of Buchan's tale starred Robert Powell as Richard Hannay, Karen Dotrice as Alex, John Mills as Colonel Scudder, and a host of other well-known British actors in smaller parts. It is generally regarded as the closest to the novel, being set before the Great War. The early events and overall feel of the film bear much resemblance to Buchan's original story, albeit with a few changes such as the re-casting of Scudder as a more immediately sympathetic character and the introduction of a love interest. It also introduces a different meaning for the "thirty-nine steps", although unlike its filmed predecessors it returns to Buchan's original notion of being an actual staircase. It is known for the Big Ben sequence near the end, inspired by the film My Learned Friend (1943), starring Will Hay, although this is its most fundamental deviation from Buchan's original story, which reaches its culmination in a coastal location in Kent.
In 1914, German spies are everywhere in London. After a spate of assassinations of important British politicians, a retired British intelligence officer, Colonel Scudder, realises his life and his mysterious black notebook are in danger. He turns to Richard Hannay, a mining engineer who is visiting Britain for a short time before returning to South Africa, who happens to be staying in a flat in the same building. Scudder tells Hannay of a plot by Prussian 'sleeper' agents, who are planning to pre-empt a war against the Triple Entente powers by assassinating a foreign minister of state visiting the UK.
Hannay reluctantly gives Scudder shelter in his flat, despite his initial distrust of him. In the morning, Hannay leaves to purchase a train ticket to his family hometown, the village of Strathallan in Scotland, while Scudder remains at work on his notes in the flat. When the Prussian agents attempt to enter the flat, Scudder flees down the fire escape but he is spotted. Posting a package containing his secret notebook in a pillar box, Scudder flees to the St Pancras railway station, where he knows Hannay will be, to give him a second black book.
At the railway station, just seconds before he can reach Hannay, Scudder is murdered by the agents. Hannay is mistaken by witnesses at the railway station as being the assailant. Hannay is arrested but is soon captured by the Prussians when transferred to jail. He then is allowed to escape from the Prussians in the hope that he can lead them to the secret notebook. Hannay manages to get Scudder's second notebook back at St Pancras, but this turns out to be a dummy, with only a three-word riddle in it that only Hannay could possibly understand to find his real book, which sends Hannay to Scotland. Hannay flees to Scotland on a train, but he is forced to make a daredevil escape on a bridge when police board.
Hannay attempts to solve the mystery whilst on the run from the police, led by Chief Supt Lomas (Eric Porter), and the Prussian agents, led by Edmund Appleton, a Prussian sympathiser highly placed in the British government.
With the aid of Alex Mackenzie and her fiance, David Hamilton, whom Hannay meets on the Scottish moors, claiming to be taking part in a wager, Scudder's book is found, the coded information partly deciphered and the true plans of the Prussian agents are revealed. The agents intend to murder the visiting Greek Prime Minister, leading to unrest in the Balkans and thus causing a world war, by planting a bomb in parliament. The "Thirty Nine Steps" refers to the number of stairs in the clock tower of Big Ben (from "Lauderdale Door to the clock itself") and Hannay realises that the bomb is to be set off by the clock at 11.45am.
When he reaches the top of the clock tower, the agents have already planted the bomb and have locked the clock room. To give the Police more time, Hannay breaks the glass of the clock-face, climbs out onto the face of the clock and physically stops the clock hands just as the big hand moves just below the nine. By hanging from the big hand, Hannay manages to jam the clock at 11.44am long enough for the Police to break into the clock room where they kill the remaining spies and deactivate the bomb. The clock mechanism stops working and the clock's big hand falls into a vertical position, but Hannay hangs on and one of the officers saves him with a looped rope. Sir Edmund Appleton is convicted of treason and Hannay is declared a hero for helping Britain gain valuable time to prepare for the Great War.
Producer Greg Smith said he wanted to make the film because he had always been a fan of John Buchan's books and wanted to do a version of The 39 Steps which was "true to the period in which the novel was set, just prior to the Great War, when Europe was one huge powderkeg and nobody knew what a world war was."
Smith claimed "the Hitchcock version was about 20 percent Buchan and 80 percent Hitchcock. Our goal was to turn it around and make the film 80 percent Buchan and 20 percent invention." Smith chose Sharp to direct "because he's one of Britain's best action adventure directors and he was familiar with the period."
Robert Powell was cast in part because of his success in the mini series Jesus of Nazareth. The script did add a romantic interest for Hannay, played by Karen Dotrice. "You can't make a movie without women," said Smith. "You can't go through life without women."
The film added a new climax with Hannay climbing on to Big Ben. Smith:
In the book, the 39 steps lead down to a beach and filmically there is not much you can do with that. Today, audiences demand more of a grandstand finish. That was the major liberty we took - the ending. People can say, 'You're not being true to the ending,' as they stay away by the millions... [Big Ben was chosen for the end] because it was an analogy we were working for - Europe was a time bomb in 1914. And we figured that the centre of European politics would undoubtedly have been the House of Commons. So we thought, 'Why not finish the film in the political seat of Britain?'
The film was the first in a series of films financed by Tony Williams at the Rank Organisation which was (temporarily as it turned out) increasing its film production in the late '70s.
"You have to go back in time to tell a story that doesn't have to face '70s problems," said Williams in 1978. "What people are nostalgic for isn't necessarily any particular period, but the happier values that are missing today."
Williams defended the idea of adapting a previously adapted novel:
The old films suffer technically against today's. The pace of modern films is much faster. The style of acting is different. Those old actors were marvelous, but if you consult the man in the street, he's more interested in seeing a current artist than someone who's been dead for years.
A replica of Big Ben was built at Pinewood Studios. The idea of Hannay dangling from the hands of Big Ben came in part from a stunt performed by Harold Lloyd in the silent comedy classic Safety Last (1923). The privately owned Severn Valley Railway loaned the film a steam engine, together with rolling stock and a section of track, for shooting.
A soundtrack album was released on United Artists Records. In addition to cues from the film, Ed Welch composed The Thirty Nine Steps Concerto, an extended piece for piano and orchestra in a vein similar to Richard Addinsell's Warsaw Concerto. Christopher Headington was the soloist, with the Rank Studio Orchestra conducted by the composer. It has not yet reappeared on CD.
The film was successful at the box office.
Greg Smith said that John Buchan's son, Lord Tweedsmuir, was pleased the film used more of his father's book, and that he thought his father would have liked the Big Ben ending.