In the bustling religious marketplace of modern America, conversions out of one faith and into another are not exactly news. They happen every day, across the full spectrum of belief. But some conversions resonate more than others, especially at a time when the U.S. finds itself at war with terrorists who draw their inspiration from one of the world's great religions.

Consider the case of Jean-Michelle Ajon, the subject of a 2002 article in the women's fashion magazine Marie Claire. Raised a Catholic in New York City, Ajon had been thinking about converting to Islam during the summer before 9/11. After the attacks, a remark that she overheard while working in Manhattan—"We should bomb everyone, the whole Arab world"—strengthened her resolve, and she soon made her shahadah (declaration of faith), thus entering the fold of Islam. Her new faith, Ajon explained to Marie Claire, had improved her life. "I used to be very aggressive," she said. "Now, I am more patient—and spiritually fulfilled."

Ajon's story—no doubt seen by her editors as an inspiring antidote to widespread anti-Muslim bigotry in the United States—has been multiplied by many other, similar stories over the past several years. But far less attention has been paid to voyages in the opposite direction, that is, outward from Islam. In fact, thousands of Muslims in the West embrace Christianity each year, and the courage they must muster to do so is of an entirely different order from the bravado of someone protesting against supposedly pervasive social prejudice. These converts stand accused, rather, of apostasy, a transgression against Islam whose consequences, even in the sheltering confines of the West, are always serious—and sometimes deadly.