Out of curiosity, is it derived from the film, or the book (or both)? I first saw the film when I was wee, and was annoyed because it seemed all different to the book[1]; only later on was I able to admit it was actually done very well.

[1] Dad: Oh, you read 39 Steps at school? Is that the one where whats-his-name trecks half-way across scotland handcuffed to this woman?
Me: No...