Captain Anorak's Guide to Gaming
Scenarios: The Situation Method
'The situation method' is the poncey name which I pretentiously give my method for writing roleplaying game scenarios. By way of preamble, let me slag off how other people do it. Many people seem to write games as a set of static, unchanging programmed encounters which the characters get to interact with. I call this 'five orcs in a room' gaming. In the stereotypical bad game of AD&D, the PCs go to a castle/dungeon/ruined tower; they fight the guard on the gate; they go in, go into a room with five orcs in and fight them; they go to the next room along the corridor and find a box full of treasure; they go into the next room along the corridor and confront the evil wizard. Most games aren't as bad as that, but the same thinking can be seen in scenario writing: each major entity in the game (eg. a non-player character or a village or a library) is one 'room' on the corridor. The player characters interact with it and then leave and go to another. These entities don't do anything by themselves, but just exist for the PCs to interact with, and they don't affect each other.

The situation method reverses the priority of things. In the situation method, the scenario is written as a 'situation' in which things are going on. Each major entity in the scenario is doing something, and thus will change over time as its course of action progresses. These courses of action interact with one another. I write out a timeline for each strand of action, noting where and when these affect each other. The important thing is that these timelines represent what would happen in each strand of action if the PCs do nothing at all. Thus, if the PCs blow into town, check into a hotel and just stay there not interfering with any plot threads, the whole thing will happen according to the written timelines. If the PCs do something, then the plot strands will deviate from the pre-written timelines and will go off and do whatever it seems logically would happen. Thus under the situation method, the major game entities are primarily doing their own things, and dealing with the PCs is only a secondary function, whereas in five orcs in a room gaming, the entities exist primarily to interact with the PCs.

In situation method scenarios, it's important that the GM keeps track of what all the plot threads are doing. This means that there'll be offstage action, events which the PCs don't get to see happening, as the threads interact. That may sound like a lot of work but it's not, and it's easy enough to keep track of.

An effect of this is that the scenario can 'finish' without the PCs necessarily causing it to finish. The NPCs in the game may resolve the situation themselves, as people would do in real life, without Our Heores getting involved. This can lead to scenarios ending in the same way many X-Files episodes end: Mulder and Scully come onto the scene just in time to witness what is happening, but aren't able to do anything about it.

What it all means is that a GM doesn't have to predict what the players have to do to make the scenario work (see forced plots). The scenario will trundle along in the absence of players doing anything.