When a film crew arrived in the small college town of Stillwater, Oklahoma last spring, few residents realized exactly what kind of movie the crew was making.

The film, which residents soon learned was called "Redeemed," was rather vaguely described as being "based on a true story of a woman's journey and God's redeeming love and forgiveness," according to local media.

The most tightly-controlled and top secret film set in the town, however, offered some clues about the film's subject matter. The film crew transformed a nondescript building on the edge of downtown into a replica of a Planned Parenthood abortion clinic.

Father Brian O'Brien, pastor of St. Francis Xavier Church in Stillwater, told CNA that he noticed some changes in his congregation after the filming of "Redeemed" began.

"I started to notice a few more people at Sunday Mass, just some people I hadn't seen before, and they were there all the time, coming to daily Mass," he said.

"And so eventually I connected with them, and they told me they were in town for the movie. Some of them were in the movie, some of them were the producers, writers."

What Fr. O'Brien already knew was that the film known as "Redeemed" was actually "Unplanned," the true story of former Planned Parenthood clinic director Abby Johnson, who eventually converted to Catholicism and became a leader in the pro-life movement.

Bishop David Konderla of the Diocese of Tulsa had called O'Brien last March to tell him that "Unplanned" was coming to Stillwater, and personally asked him to give any "spiritual support" that he could.

The filmmakers kept the film's true subject matter- abortion- under wraps during filming, to allay any potential pro-abortion protests during the film's production.

Did the people of Stillwater realize it was a pro-life movie?

"There was a general sense that that's what it was. People did not know the full extent," O'Brien said.

Although not everyone who worked on "Unplanned" was Catholic, O'Brien said he met one day with the group who had been coming to his parish, and they asked him not only if he would like to visit and bless the movie set, but also to celebrate Mass there. He agreed to all of it.

"And so what ended up happening over the course of April and May, spring of 2018, I would go over super early in the morning before they started filming for the day and celebrate Mass on the set," he said.

"It was early, and the goal was to have Mass before what was typically a 12- or 14- hour filming session."

He said the other thing he did was a simple blessing of each set every time the film crew moved to different locations around Stillwater.

The directors of "Unplanned" have been open about the fact that several bizarre incidents took place during filming involving cast and crew, including a near-death experience involving the film's lead actress, Ashley Bratcher.

(Story continues below)

"What was interesting is that the cast and crew, all throughout filming, reported kind of strange happenings," O'Brien said.

"The goal was to offer God's blessings upon this project and see if we could prevent some of that."

Though the time O'Brien spent on-site was not very long, he said he enjoyed sitting on the set while the crew was filming scenes for the movie, and to support two of the film's co-directors, Cary Solomon and Chuck Konzelman, both Catholics.

"It was on the set where I met lots of the other pastors of other churches, so I think they put out a call to any church that was sympathetic to the pro-life cause and said, 'come,'" O'Brien said.

The broader population, meanwhile, was told little about the movie until later in production.

"We only announced it here to our people at church when they needed extras for what I think is the final scene, kind of an aerial shot of a bunch of people at the park," the priest said.

"They needed extras for that, so we invited all of our people to go, and a lot of people did."

Now that "Unplanned" is out in theaters, O'Brien said his parish is doing a lot of promotion for the film. They have already bought out two theaters and expect about 200 people to come to see the movie all together.

Sheryl Lacy, operations manager for St. Francis Xavier Parish, told CNA that she helped to encourage people to come and be extras in the film, even those from communities outside Stillwater.

"It was exciting being able to say it was happening in my hometown, but it was quiet, no one talked about it because not a lot of people knew about it," she said.