Part II: Story and Structure

What I like most about ARGs is the way that the story line compels the play and provides a reason to keep playing. Most ARGs aren't competitive. Instead, players are working together to move the story along to reveal the ending. We humans like stories. We like to ask "and then what happened?" A good story keeps us asking what's next.
However, not every story will work for an ARG or every audience. Understanding the constraints you have (your audience, geography, technology, time etc) will actually help, rather than hinder, the creation of a story.  We knew that our audience would be primarily educators or people related to education so we evolved a plot that we hope they will relate to and be interested in. We wanted the gameplay to make sense with the story and for players to easily understand why they should want to solve them and why they're being presented.
When I talk to people about designing ARGs I often hear that they're intimidated by the story. "I'm not a writer." "I'm not creative." "How can you make a story about -insert discipline here-?" But you shouldn't be scared off by the challenge of creating a plot to tie your game together. It isn't strictly necessary for a good game (ie fun!) to have some kind of fictional line woven through it. Some simple game mechanics can take its place. Perhaps a point system, a scavenger hunt, a race...there are lots of common structures that we've all experienced that can work.
Because we knew most of our audience would be novice game players, we wanted a structure behind the scenes that would be familiar but still challenging. We brainstormed about the possibilities and considered many different familiar games: crossword puzzles, popular board games etc and settled on a logic puzzle. You know, those puzzles in magazines that ask you to figure out which of five people live in which of five houses which are each a different color and have a different car in the driveway. These have been around for a long time and most people have at least tried one at some point. Making this decision allowed us to jump right to the kinds of clues we could create, how they should be released, and what the finale of the game should be (shhhh! That's still a secret!)
What game structures would you try? What games do you love that you think could be used for inspiration? What stories will your audience enjoy and engage with?