Delacorte Yearling contest

I've been racking my brains for a decent plot for the Delacorte Yearling contest I mentioned last Friday. My kiddo is just starting books that would be considered MG (middle grade, ages 8-12) and I'm fairly familiar with the books available. I've read many of them, BUT the contest stipulates 96-160 typewritten pages, 12-point font. Of course, I can manipulate the font to reach the minimum or maximum requirement by simply changing it from courier to Times. And by my rough calculations that runs around 25K-40K words. Not a problem. If I could come up with a story in the next week or two, I could feasibly write this amount by the deadline of June 30, 2009.

The problem arises because . . . I GOT NOTHING by the way of plot!
This is driving me crazy!! Usually, I have too much plot, but now, I can't think of anything! AARRGGHH!! The really good MG stories have the main plot and a subplot or something that can link it into a series.
...and there are A LOT of good series all ready invented! The Magic Tree house books come to mind, though they are far less than the required word count. I need to come up with a story that is either contemporary or historical. They don't specifically say NO FANTASY, but I'm guessing the fantasy had better be a subplot or not at all if you look at the list of previous winners.

I'll take any, and all suggestions for a story plot. Oh, and my daughter says there has to be a sad part near the end (black moment, anyone?) because all chapter books have them. ;-)

Halp!
And Write On!