I’m also immensely grateful to my elite team of first readers: Darin Strauss, Susannah Meadows, Radhika Jones, Melissa Maerz, Sara Vilkomerson, and Anthony Breznican.
For conspicuous acts of kindness in support of this book, sincere thanks to Tina Jordan, Kami Garcia, Breia Brissey, Andrew Long, Bonnie Siegler, Jessica Shaw, Kerry Kletter, and Kathleen Glasgow.
Thank you to Erin Berger and Jennifer Besser, who read the earliest chapters and gave me vital encouragement. Erin and Jen are cool in too many ways for me to enumerate, but their generosity floors me.
Thank you to Hans Bodenhamer, a Montana science teacher who answered all my questions about caving and took me on a conservation trip with the Bigfork High School Cave Club. Hans and a fellow explorer, Jason Ballenksy, challenged me to be as accurate about caving—and as respectful of nature—as I could. Any and all mistakes are on me.
Thank you to the loyal friends who’ve always been there for me: Jill Bernstein, Meeta Agrawal, Kristen Baldwin, Sara Boilen, Sabrina Calley, Veronica Chambers, Betsy Gleick, Devin Gordon, Barrie Gruner, Chris Heath, Carrie Levy, Rick Porras, Brian & Lyndsay Schott, Lou Vogel, and my fellow YA authors in the Sweet Sixteens and the Swanky Seventeens. A special hat-tip to Karen Valby, who suggested the name Zoe for my main character back when other people were insisting that I name her after them. (A note from my friend Kate Ward: “I would settle for the villain.”)
I’m indebted to two gripping articles: Peter Stark’s examination of what it feels like to freeze to death (Outside magazine) and Ray Kershaw’s account of the Mossdale caving tragedy (The Independent).
My family and I moved to Montana in 2014 to be closer to my father-in-law, Dick Bevill. This book was written largely at a thrift-store desk overlooking Dick’s ranch, and it is, I hope, animated with a bit of his own questing spirit and his reverence for the natural world.
Thanks also to my intrepid brother-in-law, James Peterson, who went caving with me so I wouldn’t wuss out, and my nephew, Max McFarland, who coined the term “Struggle Buggy,” which I have borrowed for Zoe’s Taurus. Max uses it to describe his friend Nick’s junky Toyota Corolla, which resembles a car only insofar as it is car-shaped and has tires.
Finally, I would like to thank my awesome, weird-in-a-good-way children, Lily and Theo, and my sister, Susan Heger, who is the most openhearted person I’ve ever known.