by Jeffery L. Sheler.

Viking. 324 pages. $24.95.

Once aboard a plane I struck up a conversation with a guy next to me. Big mistake. He took out his Bible and started quoting the lines he’d underlined in red. He was an evangelical something-or-other. The Bible was God’s word (at least those words underlined in red), Jesus was his buddy, and they were out to save me. I ordered a martini.

Jeffery L. Sheler, a former reporter for U. S. News & World Report and its religion editor for 15 years, began his own spiritual journey as a fundamentalist at the Maplelawn Baptist Church in Grand Rapids, Mich. He has since grown out of the rigidities of the faith but is clearly keen on revealing the many facets of the evangelical movement, which is often misrepresented as a one-dimensional monolith.

The triumph of evangelical politics in the presidential election of 2004 may seem a bit tarnished now, but then it looked like a watershed. Debunking the “Red State/Blue State” simplicities of media maps, Sheler would probably agree with Richard J. Mouw, president of the Fuller Theological Seminary in Pasadena, who believes “that Jesus loves me, that there’s a God in charge of history, that there’s a book I can turn to for guidance. Now, I’ve nuanced those. But they’re still the things I hold onto for dear life.”

Sheler, in bright and nuanced prose, roams the country to interview megachurch ministers with their video-screen theatrics, $30-million annual budgets, and expanding rosters of seekers; builds concrete houses with self-described missionaries in Guatemala (I called it “Bricks for Jesus” when I did it in Honduras); explores the plethora of pious pastors in Colorado Springs; follows Christian lobbyists in Washington; attends a Woodstock-like Creation rock concert and sermon-riddled show in Mt. Union, Pa.

Along the way, he conducts a series of one-on-one interviews that really reveal most evangelicals as good, God-fearing, quasi-rational, neighborly folks. That’s all to the good and makes this a fascinating, in-depth look at a very splintered, fragmented, doctrine-disputing subculture that’s gone mainstream.

The sheer number who call themselves evangelicals and shell out their shekels to their Bible-thumping, media-savvy leaders is phenomenal. Clearly the movement meets some basic American need, based loosely on viewing a contemporary world that’s sinful, gay, abortion-intoxicated, sex-crazed and immoral.

I’m still puzzled. With all the need for helping the poor and being kind to your neighbor, why focus on abortion and homosexuality? Is it some Calvinist hangover that’s upset with bodily fluids and confuses a seed with a soul? Why the sex stuff when so much else needs real attention? I think they’re wrong, no matter how congenial, gussied up, slick-tongued and golden-throated.

Sheler’s is an excellent look at an age-old American phenomenon dressed up in new clothes. But I’ll take my son’s response any day. When he went to visit the parents of a woman he was dating in a northern Midwestern state, the father’s first question was, “Are you a Christian?”

“No,” Sam replied thoughtfully. “I’m an Episcopalian.”