Bookshelf talks to Margaret Peterson Haddix about the conclusion of her popular Shadow Children series.

How did the Shadow Children series evolve?

When I wrote the first book, I was thinking of it as a stand-alone book. After it came out, several people said they wanted to see at least a sequel, if not a whole series, and there were several discussions involving my editor, my agent and myself.

Initially we were talking about books featuring different shadow children who didn't necessarily know each other or cross paths. You've got people who've had to hide because they're illegal children; what kind of different combinations of problems would that lead to? How would people cope with that differently? After writing Among the Impostors, and realizing that I wanted to deal with the characters who had shown up in that book, it was more of a sense of progressing the story as a whole.

Why are you choosing to end the series now?

I didn't want it to go on to the point that I felt like I was repeating myself. It's funny, I feel like I've gotten a small taste of what it's going to be like when I send my kids off to college: OK, they're grown up now. They're out and off on their own.

What are you going to miss the most?

I really enjoyed writing about Luke. I do kind of have a motherly sense about him. Also, I enjoyed dealing with the issues that the characters are grappling with. What does freedom really mean, and how do you achieve it? How do you balance security and freedom? That's something we're dealing with in our country in reality, too.

Which leads me to ask, were the books influenced by current events?

I was working on the fourth book in the series, Among the Barons, in September 2001. It threw me for a loop. I thought, "OK, I am essentially writing about people who are planning to commit acts of terrorism against their government. Can I write about that now? Does this have a context anymore?" I considered the issues more seriously than I would have otherwise—and that's probably a good thing

At that time, Among the Hidden was on several state readers' choice lists. In one state, at least, there was some concern about the book being pushed to children at a time when everybody was rallying around patriotism. It kind of fits in with the whole notion of the Patriot Act and how much freedom do we give up. I certainly feel comfortable telling kids that's something worth thinking about.

How much input have fans had on the direction of the books?

In between each book, I went through a time of panic. What am I going to do next? Often things that kids suggested in fan mail or on school visits showed up in the books. When I was thinking about writing Among the Barons, there were a lot of people saying they wanted to know more about the family that donated Luke's fake ID. That was an idea that had been in the back of my mind, but they pushed it to the front. When I was beginning to think about writing Among the Brave, kids were saying they wanted to know more about Luke's brothers. I started thinking, "Well, hmmm, I could bring Mark back."

What can readers expect from Among the Free?

I don't want to give too much away, but Luke definitely gets put into some challenging situations. How's that for being vague? I had people lobbying for a happily-ever-after type ending, where they ride off into the sunset and everything's perfect. And I had other people lobbying to leave an opening to write an eighth book. I will say there's not going to be an eighth book. So that probably gives you one indication, but doesn't necessarily mean the other thing is true.

Would you ever do a series again?

I probably will at some point. It was fun to follow the characters through more than one book. I was able to pull out the minor characters and make them major characters in their own right. I was able to follow tangents that lead into their own books. I enjoyed that a lot more than I expected to.