To the Church of Scientology, Jenna Miscavige Hill is an apostate – a discredited troublemaker bent on destroying the faith in which she was born and raised.

The soft-spoken 29-year-old mother of two doesn't come across as a heretic worthy of Inquisition-era damnation.

But with Beyond Belief, her just-published coming-of-age memoir, she has challenged a church that despises criticism by making allegations about Scientology's mistreatment of its youngest adherents. What makes her defiance even more provocative is that her uncle, David Miscavige, is the all-powerful leader of the highly secretive institution.

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Ms. Miscavige Hill says Scientology makes it hard for devotees to leave the faith, and most who do depart go quietly, since the church threatens its dissidents with severe reprisals. For an insider to speak out is rare, but her testimony is rarer still: Groomed for leadership from earliest childhood, she says she has direct experience of the church's indoctrination process and can speak with personal authority about an upbringing in which child labour, family separation, arbitrary punishment and psychological bullying were sanctioned by the church.

"I want to turn this horrible part of my life into something that has a good purpose," she says. "I hope to discourage new people from being lured into Scientology, as well as helping people whose loved ones are in there. And maybe I can get to people who are inside, and plant a seed of doubt."

Ms. Miscavige Hill's story suggests that the open society we inhabit still includes enclaves where authoritarian religious values are forced on innocent children. It is hard to look away when she describes the day-to-day torments she says she suffered in a church whose beliefs and behaviours are weird even by the standards of offbeat new religions.

But then everything about Scientology is peculiarly fascinating to the rest of us: the intense cultivation of Hollywood celebrity culture, the "space opera" theology of past lives and roaming aliens created by founder L. Ron Hubbard and the extreme enthusiasm of the church's followers, who spend small fortunes on training courses that lead them through the mysteries of the faith. Ms. Miscavige Hill describes it all as "brainwashing," a cultish term that can't help but pique the sensation-seeking prurience of outsiders.

Like all new religions that face opposition, Scientology is keen to trumpet its successes and the church has embarked on a global expansion plan that includes the building of dozens of state-of-the-religious-art facilities – including a new church in Cambridge, Ont., that is being opened on Saturday, and a luxurious advanced-training resort nestled along the Niagara Escarpment northwest of Toronto. But the church's trademark optimism can't fend off a dissonant chorus of complaint that the institution has lost its way.

The mounting criticism includes Lawrence Wright's new book Going Clear, which focuses on Mr. Miscavige's courting of celebrities such as Tom Cruise and Canadian filmmaker Paul Haggis; a recent Vanity Fair article on the church's efforts to arrange a marriage for Mr. Cruise; a film, The Master, which describes the dodgy origins of a post-war therapeutic cult called The Cause; a South Park episode that casually revealed Scientology's most closely guarded secrets about the creation of wandering spirits known as thetans; and calculated cyberattacks by the Anonymous group of hacktivists.

The anti-Scientology campaign claimed a victory in Canada last April – and added to the skepticism about the future of the organization – when a church-affiliated Narconon drug-rehabilitation centre in Trois-Riviere was shut down by provincial health-care officials.

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Scientologists are trained to ignore all this critical noise. For powerful Scientologists such as Mr. Cruise, the church's rigorous teachings have undoubtedly helped them overcome doubts and find a discipline that is laser-like in its fixation on a goal.

"They sincerely believe that their lives gain purpose and meaning, and that they have superior insight into the world," says Lorne Dawson, professor of sociology at the University of Waterloo.

Mr. Miscavige has made it a priority to cultivate the church's big names, maximizing their P.R. potential and flattering them with deluxe celebrity centres and special honours of recognition – Mr. Cruise was awarded Scientology's newly created Freedom Medal of Valor in 2004.

But there's little Mr. Miscavige can do to counteract the memoir by his own niece, because it's such a seemingly matter-of-fact retelling of the indoctrination process that gives the church control over its members.

Ms. Miscavige Hill says her early childhood was spent at a remote camp in the California desert, where the third-generation Scientologist was put to 14-hour days on manual labour and the church's technical training without getting even a rudimentary academic education. She says she saw her parents, who lived at Scientology headquarters 30 kilometres away, once a week at best.

By the age of 7, Ms. Miscavige Hill says she held the job of camp medical liaison officer, responsible for tending the health of her fellow trainees. Her Miscavige name accelerated her advancement: The same year she was inducted into the Scientology's executive-leadership stream, known as the Sea Organization, and told to sign a billion-year contract with the church.

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"It's disgusting," she now says. "It's completely taking advantage of someone who's innocent, vulnerable and has no one there to protect them – who really has no idea what they're signing."

But for anyone living in the Scientology environment, where excommunicants claim the outside world is depicted as ignorant and threatening, imposing a billion-year contract was perfectly suited to the church's values.

"We believed that we were spirits called thetans who'd lived lifetime after lifetime and been around billions of years," Ms. Miscavige Hill says. "So even though your body was young, you're basically an adult."

Scientology's future leaders, she says, were expected to reveal everything about themselves in sessions with superiors and willingly inform on their colleagues' slightest deviation from the religion's norms. Early training involved practicing how to stare at a policy statement by L. Ron Hubbard for an hour or enduring two hours of being belittled in a toughening-up exercise of humiliation called Training Routine Bullbait.

Scientology, which began as a self-help movement in the 1950s, teaches its followers to disconnect their mind from their feelings, to react logically rather than emotionally. The aim is to gain control, of self and others, and to block out negative thoughts – Ms. Miscavige Hill's grandfather, an early convert, credited Hubbard's teachings about unlimited human potential with making him a top salesman.

But the "crazy, closed world" Jenna Miscavige Hill says she inhabited as she did the laundry for church executives and made beds for visiting Scientologists in church-run hotels was one of restriction, suspicion and mistrust.

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Submission to authority was prized. Outbreaks of individuality were treated as ethical violations and individual desires as disruptive signs of selfishness. Questioning and curiosity were regarded as defiant and dangerous. Those who resisted authority and conformity risked being declared a Suppressive Person – an extreme form of demonization that could require other Scientologists, family members included, to cut them out of their lives.

Outsiders, labelled wogs in church parlance, were increasingly finding fault with these manifestations of Scientology as the Internet expanded, but word of their criticisms never penetrated into the Sea Org. universe.

"Within the church, you're not allowed to have cellphones, the only access to the Internet is in a locked room, and there's special software that blocks anti-Scientology websites," Ms. Miscavige Hill says. "So if you have a bad experience, you think you're the only one who feels that way, you think you must be crazy."

Because of her relationship with the head of the church, she says, she was sometimes spoiled and pampered, such was the fear of offending her uncle. But as she matured into a friendly, too enthusiastic teenager, she was more closely monitored, making it easier for an unbearable deviation like flirting with male co-workers to be spotted and corrected through demotion and hard labour – her punishments included scrubbing mouldy bathroom grout with a toothbrush.

When her parents, fed up with being mistreated themselves, finally decided to quit the church, their daughter says, she became suspect as well and her loyalty was tested even more. At 18, she was caught having sex with her fiancé in violation of church laws, and was forced to describe every detail of the experience. Such intrusive confessionals are an essential element in the church's practices, she says, and any admissions of wrongdoing or shameful behaviour are weapons that can later be used against would-be critics.

Eventually, she too, decided she had to leave, and faced the breakup of her marriage when church officials told her husband he would be disconnected from his family of big-donor Scientologists if he joined her. She says she was also told to swear that she would never speak out against the church – each violation would cost her $10,000.

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When the church inaugurates its so-called Ideal Org. (i.e. church) in Cambridge, Ont., on Saturday, a building meant to display all that is best about David Miscavige's visionary leadership, protesters will assemble to dampen the festive spirit.

Negativity is in the air. Scientology's optimistic plans for an advanced training base northwest of Toronto – which a church publication says will include 50 rooms where members can rid themselves of past-life traumas by being hooked up to a machine called an e-meter and a fully equipped office reserved for the return of L. Ron Hubbard, who died in 1986 – also attracts online jeers and public protests from ex-Scientologists and their allies.

Former members of the church are skeptical of the need for these new centres and dozens like them that have been built around the world, even as they acknowledge the institutional logic of the growth strategy. "They're attempting to convince people that they're expanding simply by acquiring real estate," says Jefferson Hawkins, a one-time Scientology marketing expert. "They're showplaces, but they're largely empty because membership has been declining for many years."

Official Scientology membership numbers are hard to come by. The degree of commitment to Scientology can extend from a casual purchase of Mr. Hubbard's seminal book, Dianetics, or the filling out of an introductory Scientology questionaire ("Do you sleep well?"; "Do your past failures still worry you?"; "Are you often impulsive in your behaviour?") to the high-level courses that supply Mr. Hubbard's more esoteric revelations after years of study and the expenditure of several hundred thousand dollars.

Canadian Scientology leaders say there are about 100,000 members in the country, but the 2001 Census recorded only 1,525 Scientologists. Prof. Dawson estimates that there are 5,000 Canadian Scientologists, and 150,000 worldwide. Mr. Hawkins guesses that the global total is no more than 40,000 – countering claims by church officials that there are as many as eight million members.

If there is such a glaring discrepancy between low membership numbers and a grandiose expansion plan, attracting new followers to the glamorous new buildings would seem to be essential for Scientology. But some outsiders think the growth strategy could be just as much about boosting the enthusiasm and support of long-time members, particularly big donors such as Mr. Cruise, and Nancy Cartwright, the voice of Bart Simpson.

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And so the unveiling of a new facility resembles a massive Scientology pep rally. At the recent opening of an Ideal Org. in Padua, Italy, thousands of devotees celebrated the renovation of a delapidated 18th-century Veneto villa, local politicians praised the church's anti-drug campaigns and disaster-relief efforts, and the boyish-looking Mr. Miscavige made a pledge "to bring our help and the infinite wisdom of L. Ron Hubbard's technology to this region."

Such highly visible displays of solidarity aim to drown out all the ambient negativity about the faith: "There's a P.R. value externally, but there's also a P.R. value internally," Mr. Hawkins says. "Because they can say, look how well David Miscavige is doing as our leader."

But beyond the ambitious CEO's growth trajectory, there's also a deeper psychological element that holds Scientology's believers close to their faith. "You think your entire progress as a spiritual being is tied up with your progress in Scientology," Mr. Hawkins says. "You're going toward a state of immortality where you're an all-knowing being and can go from body to body, and that's a hell of a thing. If somebody says, 'You do what I say or I'll cut you off from any spiritual advancement,' you're going to tend to do what they say."

To outsiders, this kind of complete devotion may sound extreme and even self-destructive. "What we're missing is that an individual has undergone maybe a decade of what's called cognitive drift," Prof. Dawson says. "It's a process where you get drawn in and experience social reinforcement, you like the people and enjoy the activity, maybe you get psychological benefits, you feel more relaxed. Eventually, and only a small segment of people get to this stage, your mindset shifts."

But this is where Ms. Miscavige Hill draws the line: Scientology's growth strategy, she says, now depends on retaining the children of the most fervent Scientologists, people who are nurtured in the faith and accustomed to its ways.

"There are many people like myself who were born into it," she says. "They didn't have a choice and that's all the world is for them. They don't have anywhere else to go. … We weren't given a good education, we weren't taught how to drive, we don't know how to use a bank account or how to cook, and that's a really big deal."

To address those feelings of isolation and anxiety, she helped establish the exscientologykids.com website with a mission that neatly matches the It Gets Better campaign for gay youth.

"It's a place where people in Scientology who are having trouble and don't think things are quite right can visit and know that there are people out there going through the same thing," she says. When Katie Holmes split from Tom Cruise and demanded custody of their daughter, she offered public encouragement. "I was just saying, good for you, get your daughter away from there, that's no place for children."

Yet for all that she is dedicated to changing the ways of Scientology, she is still a product of the system, and she hesitates when asked if it did her good as well as harm.

"There are some truths there," she says slowly. "Scientology started out as a self-help group, and there's one thing Scientologists love to say: Communication is a universal solvent. Some things L. Ron Hubbard said may be true. But you can find those same truths in much less controlling and abusive organizations."

And then she turns back to her own experience of Scientology, the lesson she's gleaned from the 21 years she spent in the faith. "It's one thing if you go there to get help as an adult. But if you start to experience Scientology as a child, it's hard to say it's helping you solve your problems when it's also creating all of your problems. The one thing Scientology helped me with is to get over my fear of crazy Scientology executives."