The ending in the novel - apparently - which has 39 steps down:

http://en.wikipedia.org/wiki/The_Thirty-Nine_Steps

"After some reasoning worthy of Sherlock Holmes, and with the help of a knowledgeable coastguard, the group decide on a coastal town in Kent. They find a path down from the cliff that has thirty-nine steps. Just offshore they see a yacht. Posing as fishermen, some of the party visit the yacht, the Ariadne, and find that at least one of the crew appears to be German. The only people onshore are playing tennis by a villa and appear to be English, but they match Scudder's description of the conspirators, The Black Stone. Hannay, alone, confronts the men at the villa. After a struggle, two of the men are captured while the third flees to the yacht, which meanwhile has been seized by the British authorities. The plot is thwarted, and the United Kingdom enters the First World War having kept its military secrets from the enemy.

A few weeks later, Hannay joins the army with a captain's rank."


Here is HITCHCOCK's film ending:

"She leads them to Mr. Memory's show at the London Palladium. When the performer is introduced, Hannay recognises his theme music - it's the annoyingly catchy tune he hasn't been able to forget for days. Hannay puts two and two together and realises that the spies are using Mr. Memory to smuggle the secrets out. As the police take him into custody, he shouts out the question, "What are the 39 Steps?" Mr. Memory compulsively begins to answer, "The 39 Steps is an organisation of spies, collecting information on behalf of the foreign office of ...." Jordan shoots him and tries to flee, but is apprehended. The dying Mr. Memory recites the information stored in his brain, a design for a silent aircraft engine."

Here is the version that I was thinking of:

http://en.wikipedia.org/wiki/The_Thirty_Nine_Steps_(1978_film)

Plot
In 1914, German spies are everywhere. 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 live in a neighbouring apartment. 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 apartment, despite his initial distrust of him. In the morning, Hannay leaves to purchase a train ticket to the village of Strathallan in Scotland. Scudder also leaves the apartment to post a parcel, but he is spotted and follows Hannay to the railway station to supposedly give him the black book.

However, before he can reach Hannay, Scudder is murdered and Hannay is framed for the death by the 'sleepers'. Hannay manages to get Scudder's notebook, but this turns out to be a dummy, with only a code in it to find his real book, which he has posted 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 11.45.

When he reaches the top of the clock tower, the agents have already planted the bomb and have locked the clock room. Hannay is forced to break the glass of the clock-face and physically stop the clock hands, leading to the iconic final sequence.