Linear

From NWNWiki

In storytelling, the term linear describes a plot that starts in a particular place, travels through various predictable places, and ends up at a particular place. Most written stories follow this form of plot.

Interactive stories, such as a NWN module, probably should not take a strictly linear plot thread, as this can tend to be somewhat boring. In addition, in Persistent Worlds, linear plot threads are basically impossible due to the very nature of Persistent Worlds.