Transcript for Leah Remini on Her New Anti-Scientology Attack: Part 1
Reporter: What if you spent most of your life, maybe all of it, devoted to a religion that demanded much of your time, your money and your mind? It is our responsibility to be scientologists no matter where we live or work, no matter our resources, or excuses. Reporter: What if you then publicly broke from that religion, and the entire belief system that defined your world? If you're a scientologist, you see life, you see things the way they are, in all its glory. Reporter: And what if that religion then publicly denounced you, your character, and your motives? Well then, perhaps you'd find yourself talking like actress Leah remini. No one ever wants to turn around and go, "Okay, this thing I've been defending and promoting and helping was a lie." Reporter: Remini's own story arc rivals that of any character she's ever played. Born in Brooklyn, raised in the church, she would rise to stardom on the hit sitcom "The king of queens." How about this, how about this? I go over there, punch him in the head, and come right back? Carrie, no! Reporter: Like Tom Cruise and other celebrity scientologists, remini vocally supported the church. We are the most ethical group you're ever going to find, and actually, the only group that's really making change for mankind. I promoted the church. I defended the church. Reporter: The church believes scientology can liberate the invididual mind and indeed the entire human race from its current state of enslavement, by studying the teachings of it's founder, the prolific 20th century science fiction writer L. Ron Hubbard. Scientology means knowledge, or truth, study of. Reporter: Hubbard's elaborate belief system involved an alternate history of the universe, and an unique vocabulary to describe scientology's concepts and practices. He is a spirit, and he actually can exist independent of his body. This is one of the more interesting discoveries in scientology. Reporter: The church's promotional videos highlight its international efforts to, quite literally, save the world. ??? Make a difference ??? Reporter: What does it do for you, the individual? Why would I join? Well, what you would be told is that you're working to be the better, your better self in all areas of your life. Reporter: The way Leah tells it, her disillusionment with the church traces back to this man. My name is David miscavige. Reporter: David miscavige, who took over the church in 1986 after Hubbard died. They would call me a word called disaffected, which was that I was showing signs of not being in line with the group. Reporter: That disaffection has driven remini to join a group of former scientologists crusading against the church as passionately as they once defended it. The actual writings and teachings of scientology is harmful and dangerous to people. Reporter: After leaving the church in 2013, then penning a sulfuric tell-all, Leah has now taken off the gloves completely. Who are you working for? Reporter: Escalating her battle with scientology as the paid executive producer and star of a new A&E series. So, how would you describe the show? I would describe the show as a documentary on the abuses of the church of scientology. Reporter: Each episode finds the former sitcom star crisscrossing the country harvesting tales of other disillusioned ex-church members. And I went through hell. Unconditional love does not exist in sicientolscientology. I thought he was going to kill somebody. Nobody deserves to have their family torn apart because of a belief system. Reporter: The church describes the show as "Anti-religious hate speech," and has plenty more to say about remini and her confederates. They sent us this box, filled with documents, thumb drives with video. I've seen the most disgusting comments on things towards scientologists from people who have no idea what it is. Look at it yourself and don't rely on some other third party to tell you about it. Reporter: All those charges and countercharges, sometimes boying over into open confrontation. You're going to tell me that you're not a private investigator? Reporter: Dispatches from the front lines of a war without guns. You said on the show that you actually feel responsible, personally, given how much you did to promote the church. I do have a responsibility. What I'm saying is, "Hey, you're abusing people. And then on top of that, you're victimizing your victims." Reporter: The people remini calls victims are former church members who now say the church is essentially a totalitarian organization. Pressuring members to spend lots of money for courses and books, to submit without question to the church's ethics and disciplinary codes and indoctrinating them to believe that Hubbard's writings are infallible gospel. The church characterizes everything you see, on that broadcast and on this one, as a shameless attempt to profit off the defamation of scientology. Disgruntled people make better stories than happy people, so, unfortunately, that's the way our news seems to be these days. Reporter: The church points out, correctly, that ABC holds a 50% ownership stake in A&E, the network which airs remini's show. Further, the church safes, aside from this project, remini hasn't done anything remotely successful in years. Would you say that this, for lack of a better word, fight against the church, has taken over your career? Many people wish they had a hit show in their lifetime. I don't have to work. I still love what I do. But a big part of Leah, which the world doesn't know, is that I fight for people. Leah remini seems to be making a career out of attacking scientology. Reporter: Just yesterday, "20/20" sat down with Monique Yingling, an attorney for the church of scientology, for this rare on-camera interview. Let's stop, let's stop for a second. Everything she's been doing on her show has been scripted, rehearsed, acted and then dramatized. Reporter: So you think her motives here are to make money and keep herself in the public eye? Absolutely. I've heard it before. I'm going to hear it again. Reporter: But just to run this down, there is -- you do get paid. And you do get attention for doing this stuff. I don't work for free. This is a very demanding job. I'm not going to justify. They get paid. They got $3 billion in assets. I'm not saying, "Hey, I'm the savior of your world. I have all the solutions to your life." My life is pretty freaking awesome and I am functioning at a very high level. My life, in the last 12 years, has completely turned around. Come and pay me. Give me your life. Give me your money. Give me your children. Reporter: Do you think David miscavige is watching the show? Yes. Reporter: What would you say to him? Nothing. I think it's always, like, cheesy, when you guys ask these kinds of questions, like, anybody would sit and go, "Yes, I want to talk directly on the camera." Like, do people actually bite on this one? Reporter: All the time. Really? Reporter: Yes. Interesting. The only thing I hope that he hears is, I'm going to continue to tell these stories. Reporter: Lea Remy may now be the world's most famous anti-scientologist, but she's certainly not first.
This transcript has been automatically generated and may not be 100% accurate.