I've been reading -- if that's the right word, because you could also say 'playing' -- Inkle Studio's impressive e-book version of Steve Jackson's classic gamebook The Shamutanti Hills, the first volume of the Sorcery! series. The Shamutanti Hills is a game, a map, and a story: an interactive fiction in which the reader exerts choice over the path he or she takes to the end of the book.
Now, all fictions are interactive in that they involve engagement, the creation of a world between the reader and the text, and the play of speculation and imagination: guesses, expectations, and reversals. But interactive fiction enhances the possibility of interplay by giving the reader choice over the path of the narrative at key points. The most popular of these, and the ones that have interested me for some time, are those based on games and quests. The idea of a path is not incidental: the gamebook often resembles a map or chart, or even a labyrinth, where the ideal play is to find the optimal path through.
The Shamutanti Hills does a fine job at this. What I most admire about it is the sense that the hills constitute a real, if fantastic, terrain: a landscape of mines, villages, hills, woods and ruins, inhabited by goblins, giants, witches, elves and wizards, villagers and monsters, that one can pass through and explore, rather than a simple series of challenges. One feels that the stories of the hills intersect and carry on their own life, and this is enhanced by the game aspect of surviving and mastering the various challenges that the hills represent. The Shamutanti Hills rewards play because each play-through reveals something new about them.
Although the fantasy quest provides a way of structuring the forking narrative of the gamebook, I speculate that the form could also be applied to the mystery. Imagine a mystery in which the reader takes up the role of investigator, choosing clues, hunting leads, suspects, uncovering the plot (or not), building the case on the basis of decisions made in reading.