As a writer, Stevenson knows his stuff. The charcterisation of David and Alan, the two main characters, is excellent and the plot is driven forward by being in the form of a journey for survival in the Scottish wilderness. The Highlands and Islands are depicted realistically in the book and it is historically accurate (Unlike that flim with Mel Gibson in it).
When I first picked up this book I was expecting a historical action-adveture story. In fact, this novel has character driven plot and the main source of conflict is the way that David's conservative, lowland views clash with the personality of Alan, a jacobite. However, this does not put you off reading the book as this is handled very well.
Off course, the book still has action in it, as David has to cope with such dangers as kidnapping, an evil uncle who tries to kill him and torrential Highland downpours.