The novel describes the "man on the run", which would later become something of a standard in films noirs. We always identify with him and follow his adventures, and rejoice in his redemption in the end...
I said I liked Hitchcock's version, but next to the actual book, it simply pales in comparison: the book starts with a general overview of the political climate at the time - Europe is on the verge of war and various political alliances form and threaten others. It was very interesting to see (this is 1915) how well aware Buchan was of the little intrigues that were formed and how the would contribute to the deterioration of society, and I could even detect some early comments against the Jews that I could well imagine continued, increased and contributed to another war as well...
But this is just the setting of the story. Already from the beginning the plot does not resemble at all the film, and I find I like the book more: we get to know a little about Hannay first and become aware of his weaknesses and we understand better all that will ensue. The initial meeting with the victim that will trigger the rest of the plot is in the building where Hannay lives (it's a neighbour), and not in a theatre with a total stranger. All is more believable in the book, and more focused on the details that will explain the steps to follow.
I continue reading and I start getting upset with Hitchcock. He has managed to distort the plot in every possible manner. And while I understand that in a black & white film one cannot see much of nature, Buchan's novel is full of beautiful descriptions of the Scottish landscape that provide the background elements for the chase, the capture, the escape and all other action scenes with Hanney.
This is a story of a bored man (well-off, naturally and recently back from Rhodesia) who seizes the opportunity to do something for his country and thus come to realise the greatest interest one can have: the good of society in general. The United Kingdom's military secrets are in danger of being communicated to the enemies and that can have disastrous consequences with regard to its role and position in an eventual war. Given the time this novel is written, this was a well-received message for those directly involved with the war: we need to go beyond our petty, individual interests and see how and where we can help for the general good.
Of course, throughout all of his adventures, Hannay always emerges the winner: I would not have expected anything else, and although I did miss some negative spots in the story, I understand the need for such a hero. He never questions his involvement, he actually does more than his fair share, and in the end it will be him to confront the conspirators. The UK thus enters the 1st World War, with its military secrets intact and Hannay will enlist as a captain.
Despite dealing with war issues (not my favourity subject), I really enjoyed this book - especially after watching the movie adaptation and appreciating Buchan's penmanship. But also because of the humanity that can be found in all of us (Hannay encounters some beautiful people along the way), and the lack of the necessary love interest that had to be present in the movie - the novel wins!