(Providence, R.I.)  Kevin Roose managed to blend in during his single semester at Liberty University, attending lectures on the myth of evolution and the sin of homosexuality, and joining fellow students on a mission trip to evangelize partyers on spring break.

Roose had transferred to the Virginia campus from Brown University in Providence, a famously liberal member of the Ivy League. His Liberty classmates knew about the switch, but he kept something more important hidden: He planned to write a book about his experience at the school founded by fundamentalist preacher Jerry Falwell.

Each conversation about salvation or hand-wringing debate about premarital sex was unwitting fodder for Roose’s recently published book: “The Unlikely Disciple: A Sinner’s Semester at America’s Holiest University.”

“As a responsible American citizen, I couldn’t just ignore the fact that there are a lot of Christian college students out there,” said Roose, 21, now a Brown senior. “If I wanted my education to be well-rounded, I had to branch out and include these people that I just really had no exposure to.”

Formed in 1971, Liberty now enrolls more than 11,000 residential students, along with thousands more who study through Liberty’s distance-learning programs. The university teaches creationism and that the Bible is the inerrant word of God, while pledging “a strong commitment to political conservatism” on campus and a “total rejection of socialism.”

Roose’s parents, liberal Quakers who once worked for Ralph Nader, were nervous about their son being exposed to Falwell’s views. Still, Roose transferred to Liberty for the spring 2007 semester.

He was determined to not mock the school, thinking it would be too easy – and unfair. He aimed to immerse himself in the culture, examine what conservative Christians believe and see if he could find some common ground. He had less weighty questions too: How did they spend Friday nights? Did they use Facebook? Did they go on dates? Did they watch “Gossip Girl?”

It wasn’t an easy transition. Premarital sex is an obvious no-no at Liberty. So are smoking and drinking. Cursing is also banned, so he prepared by reading the Christian self-help book, “30 Days to Taming Your Tongue.”

He lined up a publisher – Grand Central Publishing – and arrived at the Lynchburg campus prepared for “hostile ideologues who spent all their time plotting abortion clinic protests and sewing Hillary Clinton voodoo dolls.”

Instead, he found that “not only are they not that, but they’re rigorously normal.”

He met students who use Bible class to score dates, apply to top law schools and fret about their futures, and who enjoy gossip, hip-hop and R-rated movies – albeit in a locked dorm room.

A roommate he depicts as aggressively anti-gay – all names are changed in the book – is an outcast on the hall, not a role model.

Yet, some students also grilled him about his relationship with Jesus and condemned non-believers to hell.

After a gunman at Virginia Tech killed 32 people in April 2007, a Liberty student said the deaths paled next to the millions of abortions worldwide – a comment Roose says infuriated him.

Roose researched the school by joining as many activites as possible. He accompanied classmates on a spring break missionary trip to Daytona Beach. He visited a campus support group for chronic masturbators, where students were taught to curb impure thoughts. And he joined the choir at Falwell’s Thomas Road Baptist Church.

Roose scored an interview with the preacher for the school newspaper, right before Falwell died in May of that year. Roose decided against confronting him over his views on liberals, gays and other hot-button topics, and instead learned about the man himself, discovering among other things that the pastor loved diet peach Snapple and the TV show “24.”

Roose would duck away to the bathroom to scribble down anecdotes or record them during lectures. He never blew his cover, even ending a blossoming romantic relationship rather than come clean. He revealed the truth on a return trip to campus. He grappled with guilt during the entire project, but said he ultimately found forgiveness from students for his deception.

“If he told me he was writing an expose or maybe if the book turned out to be what I considered unfair, then I might have been more troubled,” said Brian Colas, a former Liberty student body president who befriended Roose.

The university administration has been less receptive. Chancellor Jerry Falwell Jr. said in a statement that Roose had a “distorted view” of Liberty before he arrived and gave an incomplete portrait of the school.

“We appreciate Kevin’s generally positive tone toward LU but he admittedly comes from a culture that has very little tolerance for conservative Christianity and even less understanding of it,” Falwell said.

Roose said his Liberty experience transformed him in surprising ways.

When he first returned to Brown, he’d be shocked by the sight of a gay couple holding hands – then be shocked at his own reaction. He remains stridently opposed to Falwell’s worldview, but he also came to understand Falwell’s appeal.

Once ambivalent about faith, Roose now prays to God regularly – for his own well-being and on behalf of others. He said he owns several translations of the Bible and has recently been rereading meditations from the letters of John on using love and compassion to solve cultural conflicts.

He’s even considering joining a church.