New York Times bestselling author Ruthie Knox and Library Journal–recognized author Mary Ann Rivers exchanged tens of thousands of emails, texts, words over the phone, and manuscript pages before a single provocative email exchange dared them to direct the energy and love in their conversations into a story. Soon, a shared intelligence they dubbed “Third Brain Mill” had written a book and started another. They haven’t looked back, and they dare each other and their Third Brain Mill regularly — usually while taking a walk together.