The main device in Kidnapped is that David Balfour narrates the entire text.

The reader knows only what he knows and tends to believe what David believes. Thereby an element of realism is developed, in that the headlong plot is not slowed by deep thoughts and profound speculations, such as might be expected from the author himself in a third-person narrative or from a more sophisticated narrator. David tends to believe what he is told, at least for the first several chapters. As he becomes more aware of the machinations of his enemies, he grows more wary, but in a quite credible manner. For example, in the early scene in which the wicked uncle, Ebenezer Balfour (it has been speculated that Stevenson used his mother's maiden name as something of a tribute to her), tells David that he must lock the lad out of the house while Ebenezer...