Kidnapped

For what it's worth, I just finished Stevenson's "Kidnapped". Telling of poor young David Balfour who firstly gets kidnapped and then is chased across Scotland for a murder he didn't commit, it's a quintessential adventure narrative and obviously a big influence on so much popular entertainment that was to follow (particularly movies). For instance in its use of a wild landscape to backdrop fugitives on the run, you can really see where a far inferior work such as "The Thirty Nine Steps" comes from. More obviously, it is one of the first great 'buddy' stories; you know, the "Midnight Run" kind of thing where chalk and cheese types forge a bond as they're chased across country. This is one of the first, and best, examples of that particular staple.
As Stevenson fiction goes, I personally prefer "Treasure Island" (a real childhood favourite) as a young person's adventure story, and "Jeckyll and Hyde" is my all-time favourite Stevenson novel, but "Kidnapped" is a good 'un. Now if only they'd told me there was a sequel!