A young woman from a polygamous and incestuous breakaway Mormon sect is speaking out for the first time after she exposed what the government alleges is a multimillion-dollar fraud, ripping off taxpayers.

Mary Nelson, 23, tells "Whistleblower" host Alex Ferrer about how she escaped the Kingston clan, also known as The Order, with the help of her boyfriend Bryan. They got married and contacted the IRS and FBI, helping uncover the alleged a $511 million scam.

The episode, "Polygamy, Power and Profits: The Case Against the Kingstons," airs Friday, May 31 at 8/7c on CBS.

"Mary, who are these individuals?" Ferrer asked Mary Nelson, holding a photo of her parent's family.

"Those are all my siblings," she replied.

"Do you miss them?"

"Yes, I miss them very, very much," she said,

"When I found out that Mary's father had … over 200 children, I knew something was very wrong," said Bryan Nelson.

"My father has 18 wives," said Mary Nelson, who is telling how she became an unlikely whistleblower against prominent members of her own family -- the Kingston clan.

"They'd give you instructions. They say, 'Don't ask questions,'" she told Ferrer.

On Feb. 10. 2016, after going to the federal government, a series of events that Mary Nelson helped set in motion, exploded.

As KUTV reported in February 2016, "A major show of a force at several … businesses owned by the Kingston polygamous group."

The raids were part of an investigation into an alleged money-laundering scheme funding lavish lifestyles of some prominent Kingstons, from mansions to exotic cars, while other members live near the poverty line.

"It was more like an organized crime family," said Mary Nelson.

Mary might never have become a whistleblower if she hadn't met Bryan Nelson, a fellow student at Salt Lake Community College who helped her escape the clan after she says she was ordered to marry her 17-year-old cousin.

After the escape, the couple married and eventually had two children.

Mary told Bryan what she had seen while working at the Kingston's own private bank.

"Did you forge documents when you worked there?" Ferrer asked Mary.

"Yeah," she said. "So, we were given just stacks and stacks of checks, and just signing them, signing them … and they would just deposit that and … just whatever account they needed."

Washakie Renewable Energy appears to be the most profitable business owned by group members.

"So, when Mary was telling me -- this is the biggest company that the Order has, I started to immediately suspect fraud," Bryan Nelson explained.

According to the government, Washakie's founders, brothers Jacob and Isaiah Kingston, falsified the company's tax filings to obtain a massive $511 million worth of fraudulent tax credits.

"Right then and there, I said, 'We got 'em,'" Bryan Nelson said, "that's the beginning of the end."

"There was nothing that was going to get in my way of stopping this," he added.

"What made you decide to become a whistleblower?" Ferrer asked the couple.

"We didn't know that that's what we were. We knew that something had to change," said Mary Nelson.

"What kind of harassment did you and Mary receive?" Ferrer asked.

"So, it began with just like cars parked down the street right, just watching us," Bryan Nelson explained. "Then all of a sudden, there was vandalism. Then there was a brick thrown through our window."

"Were you ever afraid that the Kingston group would find out that you and Bryan were the informants who went to the FBI?" Ferrer asked.

"I'm still very, very scared about that," said Mary Nelson.

"You were afraid that they were going to hunt you down," said Ferrer.

"Yeah," she replied.

The two Kingston brothers and their business partner, Lev Dermen, are in jail awaiting trial, scheduled to start in July and last six weeks. Sally Kingston, a wife of one of the brothers, and Rachel Kingston, the brothers' mother, are not in jail but they were also indicted and are scheduled to join the brothers at trial.

Mary and Bryan were and still are very worried about retaliation. Court documents reveal text messages from Jacob Kingston relating to an "enforcer" he allegedly hired, where he asks about "bulk discounts" and a "2 for 1" deal, plus other comments that appear to point to Bryan and Mary. The government alleges the brothers hired the enforcer to intimidate and harm potential witnesses -- and those witnesses could very likely be these whistleblowers.

In response to a CBS request for comment and an interview, the Kingston group said they "condemn in the strongest terms fraudulent business practices and stress that this behavior goes completely against our beliefs and principles." In addition, they say "business owners who are members of the [the group] have the autonomy to make their own business decisions."