There are all sorts of ways for two author to co-write a single novel. In the case of Greer Hendricks and Sarah Pekkanen, they write everything together. Every chapter, every sentence, every word. “It’s not unusual for us to come up with an identical thought or word choice at the exact same time,” they elusively tell interviewers who want to know more about the process. Last year’s psychological thriller The Wife Between Us was a runaway bestseller, and follow-up An Anonymous Girl just debuted at #1 on the New York Times Best Sellers list.