AS Jenna teetered on a tiny window ledge high above teeming LA traffic, she felt she had nothing to live for.
She says: "Scientology had destroyed my life and taken away everyone that I cared about - my parents, my brother, my friends.
"Now they were trying to take away the boy I loved and I just couldn't let them do that. I was ready to jump. I had nothing left to lose."
Frantic church elders, terrified of what their boss, Jenna's uncle David Miscavige would think, scrambled to pull the distraught 17-year-old back inside to safety.
"The Scientologists are paranoid about bad publicity, so the last thing they needed was the leader's niece leaping into the traffic in the middle of Hollywood Boulevard," says Jenna Miscavige Hill, who had been terrified about being separated from her boyfriend Dallas.
Four years later she found the courage to leave the secretive organisation she was born into.
Now Jenna has written a memoir about growing up as an elite member of the church that counts Tom Cruise and John Travolta among its devotees.
The book makes explosive claims about the church, which Jenna reckons made her life a misery.
The mum of two believes Cruise's six-year-old daughter Suri had a lucky escape when mother Katie Holmes filed for divorce.
She says: "I don't know what will happen to Suri in her relationship with her mother but I know the Scientologists tore my family apart."
Jenna, now 29, knew little about the outside world until she was 20. Sent to a church outpost in Australia, she went on the internet for the first time and discovered negative stories about founder L Ron Hubbard and her uncle David.
She says: "I had been taught to question nothing.
"Growing up, when I did ask questions, I was punished. When I disobeyed them by falling in love with Dallas, they had me followed everywhere.
"I couldn't even go to the bathroom alone. I was forbidden to pick up the telephone just in case my parents - who had left the church by then - tried to call. Their letters to me were intercepted."
Jenna's memoir, Beyond Belief: My Secret Life Inside Scientology And My Harrowing Escape, paints a shadowy picture of the group's elite Sea Org inner circle.
"I was born into Scientology," says Jenna. "When I was two my parents joined the Sea Orgs and were away working 14 hours a day. I was brought up in a Scientology nursery.
"Looking back and with children of my own now, it was terribly cruel but I didn't know any different.
"I clung to my brother Justin, who is eight years older. By now we were living at a ranch in the California desert with 80 other kids. We lived in dormitories with seven other kids.
"Two dormitories shared one single shower cubicle.
"By the age of six I was assigned to outdoor chores. I was part of a chain gang breaking rocks in a river bed.
"We had to do that for four hours on weekdays and 12 hours on Saturdays.
"Weather conditions were extreme. It was either below freezing or over 100°F. The manual work would have shattered a grown man.
"Our so-called schooling amounted to 35 hours a week. Classes did not end until 9pm but most of it was mind-numbing exercises, constantly repeating quotes from Hubbard."
Jenna was seven - and barely able to read - when she was asked to sign a billion-year contract to devote her life to the Sea Org squad, because "we come back lifetime after lifetime."
From then on Jenna reckons she was expected to dole out punishments to younger kids for petty crimes like not keeping dorms tidy.
Repeat offenders were forced to sleep on a thin mattress in a bat-infested, pitch-black cellar. Daily "cleansing" involved drinking a nauseating concoction of vitamins that tasted like "smelly feet".
And when it was suspected that Jenna had been given pain-killers, she had to go through a bizarre purification ritual, sitting in a baking sauna for five hours straight, drinking pure vegetable oil and swallowing handfuls of vitamins.
At 13, Jenna says she had her first full "lifestyle audit".
She had to fill in dozens of forms about her sex life - even though she barely knew the facts of life.
Elders demanded to know every impure thought and asked if she had masturbated or had homosexual feelings. "This is the stuff they use for blackmail," she says. "I was 16, a difficult age for anyone, when I got to know Dallas. Scientology allows you to kiss but you cannot have sex before marriage.
"We broke the rules, found ourselves somewhere private and had sex. We were desperate to get married but the leadership refused it.
"Then they discovered we'd had sex. They ripped Dallas away from me, saying he had to be purged.
"That's when I climbed out of the window. They pulled me in and finally said we could get married.
"We got married at midnight in the garden of the Celebrity Scientology Centre in Los Angeles. None of my family was there.
"Immediately after the ceremony I was sent back to work - there was no honeymoon night. Married Sea Orgs can have sex but they are not allowed to have children."
And she claims: "I didn't get pregnant but several of my friends did. They were forced to have abortions, often on multiple occasions."
Forced abortions are something which Scientologists deny happens.
Jenna says: "I assumed I would never have children but we were sent to work in Australia and for the first time I met people outside the church. One woman I became friendly with had the most adorable little daughter.
"That's when it really hit me how much I was expected to give up for the church.
"Dallas and I broke a few more rules - we watched television and logged on to the internet for the first time. I managed to get in touch with my parents.
"We started talking on the phone and working out a way of escape. Of course, we were still being watched and the church found out what we were doing.
"Then Dallas and I got in our car and drove away. We haven't looked back since."
Now living in California, the couple have taken to the internet with gusto.
Jenna runs exscientologykids.com, a website to help other children caught up in the movement and Dallas, now 33, is an IT consultant.
They are also the parents of Archie, four, and 11-month-old Winnie - the beloved children they once feared they could never have.
The jargon
Here is a brief summary of the meanings of several obscure terms which are used in Scientology...
Auditing: A process in which Scientology members are grilled on all aspects of their lives
Bridge to Total Freedom: The canon of Scientology doctrines, referred to as "the Bridge"
Cadet Org: The Sea Org (see below) for children and for the children of Sea Org members
Counter Intention: Acting or even thinking against the church's teachings or beliefs
MEST: Acronym used for Matter, Energy, Space and Time – the physical universe
MEST work: Manual labour
Non-Enturbulation Order: An order issued to you if you are very close to being thrown out. It warns you that if you upset anyone else, or if the "ethics officer" receives bad reports about you, you will be in serious trouble
Overt: A sin, or crime
Sea Org: The elite, around 6,000 of the church's most dedicated followers
Suppresive Person: Used to describe those whose acts are seen within the church to have damaged Scientology
