I sort of wrote myself into a corner at the end of the second Boomer Sisters book. The story ends with the girls receiving a letter from their grandmother who lives in NY City, letting them know there is "a mystery" and asking for their help. I think there might be a graffiti artist leaving puzzling messages around the city. But what will he write and what will it mean? That's still a mystery to me...But, the story is slowly starting to take shape and I'm beginning to get a sense of what the book will be about. I've always known it would be a Christmas story, set in NYC. Thanks to my oh-so-clever ending of Book 2 (he said wryly), I've always known the mystery has to be non-urgent... that is, it has to be present in the summer, but last until Christmas. And recently I decided two of the main themes will be patience and the importance of pleasure, which both fit nicely with the Christmas theme and the lingering nature of the mystery. It's almost like I planned it, even though I didn't.
The overall series is coming together too. After finishing the second book, I realized the first book was set in the fall, the second in the summer, the third in winter... so the fourth (and probably final) book will take place in the spring. That's very appropriate for me, because I've always thought of spring as a time of endings - the end of school, the time right before we move, etc. Despite the flowers (and my March birthday), spring has always been my least favorite season.
So - research for Boomers #3 has begun. I'm reading Aristotle's Ethics (book 5 talks about pleasure & pain), scouring G.K. Chesterton's writings for appropriate quotes, researching graffiti, and I've even tracked down a serial story the Boston Globe ran in the summer of 1999, titled The Boston Tangler. Great turn-of-the-century story about a long-term, city-wide mystery... might be some nuggets there.
NaNoWriMo 2007 - here I come! (and don't worry - I'm not actually writing anything yet!)