DeWitt knew what she wanted: for him to pray for her brother. It was the kind of call he had taken many times during his 25 years in the ministry. But now he found that the words would not come. He comforted her as best he could, but he couldn’t bring himself to invoke God’s help. Sensing her disappointment, he put the phone down and found himself sobbing. He was 41 and had spent almost his entire life in or near DeRidder, a small town in the heart of the Bible Belt. All he had ever wanted was to be a comfort and a support to the people he grew up with, but now a divide stood between him and them. He could no longer hide his disbelief. He walked into the bathroom and stared at himself in the mirror. “I remember thinking, Who on this planet has any idea what I’m going through?” DeWitt told me.

As his wife slept, he fumbled through the darkness for his laptop. After a few quick searches with the terms “pastor” and “atheist,” he discovered that a cottage industry of atheist outreach groups had grown up in the past few years. Within days, he joined an online network called the Clergy Project, created for clerics who no longer believe in God and want to communicate anonymously through a secure Web site.

DeWitt began e-mailing with dozens of fellow apostates every day and eventually joined another new network called Recovering From Religion, intended to help people extricate themselves from evangelical Christianity. Atheists, he discovered, were starting to reach out to one another not just in the urban North but also in states across the South and West, in the kinds of places­ DeWitt had spent much of his career as a traveling preacher. After a few months he took to the road again, this time as the newest of a new breed of celebrity, the atheist convert. They have their own apostles (Bertrand Russell, Richard Dawkins, Christopher Hitchens) and their own language, a glossary borrowed from Alcoholics Anonymous, the Bible and gay liberation (you always “come out” of the atheist closet).

DeWitt quickly repurposed his preacherly techniques, sharing his reverse-conversion story and his thoughts on “the five stages of disbelief” to packed crowds at “Freethinker” gatherings across the Bible Belt, in places like Little Rock and Houston. As his profile rose in the movement this spring, his Facebook and Twitter accounts began to fill with earnest requests for guidance from religious doubters in small towns across America. “It’s sort of a brand-new industry,” DeWitt told me. “There isn’t a lot of money in it, but there’s a lot of momentum.”

Not long ago, the atheist movement was the preserve of a few eccentric gadflies like Madalyn Murray O’Hair, whose endless lawsuits helped earn her the title “the most hated woman in America.” But over the past decade it has matured into something much larger and less cranky. In March of this year, some 20,000 people marched through a cold drizzle at the “Reason Rally” in Washington, billed as a political debut for the movement. A string of best-selling atheist polemics by the “four horsemen” — Hitchens and Dawkins, as well as Sam Harris and Daniel Dennett — has provided new intellectual fuel. Secular-themed organizations and clubs have begun to permeate small-town America and college campuses, helping to foot the bill for bus and billboard ad campaigns with messages like “Are You Good Without God? Millions Are.”