Einstein’s real genius was in his thought experiments. He imagined what it was like to travel through the universe at the speed of light, and that imagining became the basis for his theories of relativity. I am no Einstein, but as a creator of stories, I do practice a similar process, asking myself, “What would happen if…?” That’s where the story starts.

A fifteen-year old girl from L.A. who grew up in the foster care system and drives across the country with her nine-year old brother is not an apt description of who I am or what I have done. But it’s the story I tell in Now You Say Yes. A thought experiment is at the heart of the book.

Where did it start? Seven years ago, my fourteen-year old niece, visiting from Los Angeles, said she would like to visit us in Massachusetts more often, but that airplane tickets were too expensive.

“You could drive!” I suggested.

“Uncle Bill,” she rolled her eyes. “I don’t have a car. I’m fourteen.”

“But what if you did?” I asked. Her eyes grew wide and she laughed.

That was the beginning of the thought experiment. Over the next year or so, I kept a notebook in which I asked myself questions and tried to answer them. During classroom visits to schools I would ask the kids about the story. Why would a fourteen-year old girl have to drive three thousand miles? (She became fifteen as I developed the plot.)  What problems would she have? How would she overcome them? The students were most concerned about how she would pay for gas, and what would happen if she got stopped by the police. In fact, these are two of Mari’s biggest problems, and the students had many interesting solutions, including robbing a bank, which Mari does not do.

Over a period of months, I answered one question after another, including the one that vexes all people who write for children—what to do with the grown-ups? Grown-ups, especially loving ones, will mess up a plot, since they can’t help but want to fix things, and adults fixing things is a bad idea in a book for children. One way or another, we have to get them out of the picture so the protagonists can live on their own terms. I remember Betsy Byars telling me gleefully that she got rid of five adults in one chapter. If Mari was going to drive across the country, she needed to do it without grown-ups. And so, she loses them—the ones she doesn’t trust, and the ones she does. She is on her own.

Part of the development of Mari’s “aloneness” was the decision to make her a kid who had spent time in the foster care system. I wanted the book to be about how we give ourselves identity, and so I decided to start with someone whose identity is in question—someone who’s not quite sure where she is from and where she belongs. That led me to the foster care system, and a deep dive into the way it works. I got some help from professionals familiar with its geography, a lot of reading and research, and talks with families and individuals who had been through it. So, that’s where Mari starts.

Would Mari be alone for the whole trip? I just couldn’t see her spending all that time in the car by herself, and so someone else had to come along, and that was her brother Conor. In many ways, Conor’s world becomes the soul of the book. I don’t remember why or when Conor became a person on the autism spectrum, but my discovery of him led me to an exploration of the world of autism. I was lucky enough to know a couple of families who have raised children on the ASD spectrum, and I also benefited from the sage advice of a friend, Barry Prizant, who is accomplished in the field. In that process, I came to see the world through different eyes and understand that we are all, at some level, “on the spectrum.” The writer is changed by the writing.

The last major element in the story appeared when I decided I needed to drive across the country myself, tracing Mari’s route from Los Angeles to Lynn, Massachusetts. As I planned the trip, I realized I would be driving the week of the “Great American Eclipse” in 2017 and would be in a position to see the total eclipse somewhere in Missouri. Suddenly, I knew Mari and Conor would see it, too, and many things came together, including a deadline which gave urgency to their trip. My trip was not as eventful as theirs, but I’ll never forget it.

Like many authors who spend a lot of time with their characters, I found that Mari and Conor became very real to me. Sometimes they made me laugh, and sometimes they surprised me with their behavior and with their insights and comments. I have grown to love these two kids and feel protective of them. But I’ve had my time with them, and now it is up to readers to have their own thought experiments, imagining the details of Mari and Conor’s trip, and what might come after.

Now for the cover. For an author, getting to see the cover of your new book is a little like Christmas. You’ve been waiting a long time, and you don’t know what you’re going to get. I mean, it could be a pair of socks from Aunt Edith. But it could be the forty-seven gear bike you’d only dreamed of. Pierre-Emmanuel Lyet’s cover for my new book Now You Say Yes is the super-bike, with rockets attached to the side. To my eyes, it captures the story perfectly on a number of different levels—two kids in the middle of a crowd, standing out but still part of something bigger, experiencing something spectacular. It captures the feel of the trip and who Mari and Conor are—their singularity and separateness, along with their belonging. I could not be more delighted with it.

Pierre-Emmanuel—thanks. A lot.

The cover makes me want to read the book. Hah. I did. A thousand times. Now someone else can.