As a teenager, Korean-American writer R. O. Kwon experienced the sea change that would forever haunt her: She lost her faith.
Until the age of 17, Kwon was a fervent Catholic like the rest of her family and even considered becoming a missionary when she grew up. But "gradually and then all at once", she began to realise that she no longer believed in the god she had been taught about, nor the religion that had underpinned her entire existence.
"It was terrible and wrenching," says the 35-year-old over the phone from her home in San Francisco. "Even today, I still find it incredibly difficult in some ways. But I didn't feel I had an option. I did not believe the tenets any more, so I had to leave."
She poured her anguish at losing her faith into her debut novel The Incendiaries, in which two American college students - Will, an ex-Christian fundamentalist from an impoverished background, and Phoebe, a party girl who has just lost her Korean immigrant mother - become entangled with Jejah, an extremist cult.
Kwon, whom The New York Times picked as a "writer to watch this summer" earlier this year, spent 10 years working on the novel.
This includes two years just writing the first 20 pages, which she eventually threw out. She was in obsessive pursuit of what she calls "lexical inevitability", a state in which she could pick up the book at random, read a sentence and not want to change a word.
"Such an inefficient way to go about it," she sighs. During the writing process, she would change the font or even record herself reading the lines and play them back to see if they still worked when they looked or sounded different. "I want a sentence to feel as if it could not have been any other way."
Kwon, who is married with no children, was born in South Korea and moved to the United States with her family at the age of three. The "R" in her name stands for Reese, the first name she goes by, while "O" stands for Okyong, her Korean name.
Part of her family is from what later became North Korea, which found its way into her book though she did not intend it to. The leader of Jejah, an enigmatic activist called John Leal, is said to have spent time in a North Korean prison camp.
"Everyone I know escaped before the start of the Korean War, but I have distant relatives in North Korea I have never met," she says. "Because of that longing for something I don't know anything about, I was reading everything I could get my hands on about North Korea, but of course there is so little information that makes it out."
She remains close to her religious parents, who work in real estate. They were "devastated" when she turned agnostic, but she adds that her family have said they love the book.
Although she loved writing from a young age, she majored in economics at Yale University because she thought that would give her a stable career. "I'm an immigrant, my parents are immigrants - I thought I needed that kind of insurance as an adult."
Seven months into her job at a management consulting firm, she realised she was miserable. She quit and applied to graduate writing programmes.
During the decade she spent working on her novel, she sustained herself via writing residencies, as well as freelancing and working for a short time at a literary agency.
She is now two years into her next novel, which is about women artists, ambition and desire.
Books by Korean-American female writers have been in the headlines in recent years, from Min Jin Lee's epic historical novel Pachinko (2017) to Jenny Han's young adult romance To All The Boys I've Loved Before (2014), which inspired a popular Netflix film adaptation this year.
Kwon is proud, she says, of being labelled a Korean-American writer - "even though in America, no one ever talks about how straight white male writers are straight, white and male" - and hopes to help that community grow.
"I grew up with so few Asian-American writers to read - in fact I didn't read Korean-American writers until college. It is very important to me that my books feature Korean-American characters and it's a priority to lift up other Korean-American voices."