Grandfather's Dance brings to a close the five-book series that began with Sarah, Plain and Tall, winner of the Newbery Medal and inspiration for a series of films starring Glenn Close.

When you first introduced the character of Sarah in Arthur, for the Very First Time (1980), did you ever think her story would continue to grow as it has?

No, I didn't. I did [Sarah, Plain and Tall] and someone said, "Are you going to write more?" and I said, "No, I don't believe in that." When Glenn wanted to do another, I think that's what did it.

How did the series evolve?

I have a whole history in my head. I know what happens to the people when the book ends. That landscape [in the Sarah books] is part of my past, my father's farm, my mother's life. It was very personal for me, which makes [its conclusion] bittersweet in a way.

What surprised you most, as you developed Sarah's story line?

I like the fact that the characters are imperfect. Being married to a psychologist, I realize that I learn more from imperfections. They're more touching: when grandfather loses his temper or Sarah gets stubborn. That's where the breakthroughs come, and often they come through the children, because children speak the truth. Caleb says what people are afraid to say, like, "Will she [Sarah] stay?"

What will you miss most about these characters?

I feel they will live on with me. Give me another year and I could come up with more and more plots, but this [fifth book] just seemed to have a rounded feeling; the family has come full circle. I thought Anna would grow up to be a writer, but, no, she's a nurse because she's a caretaker. Caleb will be a teacher; he's a caring person, he's patient and he's kind—that came through when he was teaching his grandfather to read. My father started teaching in a one-room schoolhouse when he was 19, so Caleb will be there soon. Cassie will be the writer.

What are you working on now?

I'm working on a bunch of things with my daughter, Emily. And I'm doing a novel, [featuring] a whole other family, in which a child dies. This feels dark. Emily reminded me that all of my books are dark; parents disappear and people leave babies places. I'm on chapter eight, and he hasn't died yet.

What made you decide it was time to wind down the series?

It naturally came to an end, but it's bittersweet because I love this family. My father died a couple years ago at age 102, and this was his little dance.