But often writers want to expand the thriller form, work on a larger canvas. This is a good idea; a bigger scope pressured into the black hole of the thriller form makes for a bigger explosion. There are all kinds of techniques for doing that.

But one approach to expanding the thriller I would caution you against - at least if you want to sell your script to Hollywood - is writing the political thriller.

A political thriller is a thriller in which the crime and the danger have a national or international source and implications. Examples include The 39 Steps, The Third Man, The Parallax View, The Manchurian Candidate, Three Days of the Condor, and All the President's Men.

Some very good movies there. But political thrillers are usually much less popular than regular thrillers for five main reasons.

1. The national and international implications are often too complicated to explain and make real to the audience in the film medium - at least in Hollywood mainstream films that emphasize speed over content.

2. Political intrigue is a shadow world that few can identify with.

3. The opposition is a vast system that is almost impossible to focus.

4. The opposition is so powerful that the hero is reduced to the lowest level; he or she is often just a chased rabbit.

5. Political thrillers typically end badly, with the destruction of the individual by the all-powerful system.