I last read this when I was 10. That was… a long time ago. It came as a surprise when the book arrived in the post to see how slim it is. A very pleasant surprise given my tirades in another place. Even more so because it is the kind of book that you can (as I did) sit down and read in one go.
Which leads me to another remarkable thing. I last read this book when I was 10. Granted, I have seen various (and mostly botched) movie versions (including that truly awful TV remake recently); but I remembered it all vividly. And I still enjoyed it. Which just goes to show what an impression it made on me at the time and perhaps goes some way to explaining why I am so intolerant of badly written books.
Buchan wrote this book as something to do whilst he was recovering from an illness (as one does). It is meant as nothing more than light entertainment. And it delivers. But it delivers extra as well. As entertainment it works because the story taps into the zeitgeist (of 1914) and rattles along at breakneck speed. It is one of the earliest of chase thrillers and also an early example of an espionage thriller. Many books (and films) have used the format since.
As well as being an intriguing story, it is well written. The minor character sketches are well drawn and Hannay is sufficiently rounded (and flawed) to make him a credible hero. And the whole is leavened with sufficient dry humour and self-doubt to make the credible hero a human being. Criticism has been levelled at some of the assumptions made by the book, but these are character traits rather than any underlying theme and, indeed, there are characters (Hannay included) who refute such assumptions.
If you are looking for a good yarn free of unnecessary plot twists, you could do a great deal worse than this.