NORTHAMPTON, Mass. — In every line of work, there are family businesses. But no business is more defined by dynasties and nepotism than evangelical preaching. Lyman Beecher, Bob Jones, Billy Graham, Oral Roberts, Robert H. Schuller, Jim Bakker: all had sons who became ministers.

It is never easy stepping into Dad’s shoes, of course. But when the family business is religion, it is especially perilous. That is one of the central laments, anyway, of “Sex, Mom, & God,” a new memoir by Frank Schaeffer. To secular Americans, the name Frank Schaeffer means nothing. But to millions of evangelical Christians, the Schaeffer name is royal, and Frank is the reluctant, wayward, traitorous prince. His crime is not financial profligacy, like some pastors’ sons, but turning his back on Christian conservatives.

Mr. Schaeffer, who is now 59 and lives north of Boston, grew up in L’Abri, a Christian community in Switzerland founded by his parents, Francis and Edith Schaeffer. In the 1960s, L’Abri was known in Christian circles as a drop-by haven for intellectually curious evangelicals, who could live in the mountains for a few days or even a few years, talking with Francis and Edith about the Bible, Christian art or existentialism. Mr. Schaeffer grew up surrounded by heady talk and, as he discusses in his memoir, tempted by the young women who passed through. He got one of them pregnant when he was 17, then married her.