Twice a day, every day for almost a month, Angie Kim and her then-two-year-old son would enter a hyperbaric oxygen tank, and be sealed inside. Kim’s son had ulcerative colitis, a condition that caused him great pain, and the constant vomiting had left him underweight. The theory behind hyperbaric oxygen therapy (HBOT) goes that if damaged cells need oxygen to heal, immersing a patient in pure oxygen will accelerate healing. Although the experimental treatment was not FDA-approved and has no proven benefits, it was a last resort Kim was willing to try.

Her son called the tank “the submarine”, and he wasn’t far off: when the hatch was closed, the dim, warm space, lit only by flickering episodes of Barney and Sesame Street outside the portholes, could almost have been underwater; Kim, 15 years on, likens it to confession. As the children watched TV, the bored caregivers and parents, wearing only cotton clothing and liberated of their potentially flammable glasses, underwire bras and belts, began to talk.

There, Kim found a window into other peoples’ lives. One of the children was a fecal smearer, which could interrupt a “dive” as they all filed out for the tank to be cleaned – which could set off another child, who’d violently bang his head against the wall. She began to feel guilty: though her son was in pain, the other children were mostly severely autistic or disabled and for their parents, HBOT was a stab in the dark for children who couldn’t walk, talk or hug. “I had always thought of myself and my family as the unlucky ones,” the author, now 50, says. “That son was also deaf in one ear and had coeliac disease. My other son had anaphylactic food allergies. I couldn’t work because of all the CT scans, MRIs and specialist cooking I needed to do. So I felt really sorry for us until I met these families, who were so upbeat. It made me have such a totally different outlook on life, the relativity of happiness.”

Her debut thriller Miracle Creek centres on that relativity, and the explosion of a HBOT tank, which injures many and kills two, one being Henry, a severely autistic boy. As new details are unearthed by shark-like lawyers, characters go from “hero to murderer in an hour” and the truth becomes more and more unfixed as gossip spreads in the small town. But for Kim, the explosion was “a Trojan horse, a MacGuffin” that gave her space to explore deeper issues: the identity crisis among migrants in the US, the realities of severe autism and chronic illness, and the extremes of parental sacrifice.

Of the latter, there are plenty. Elizabeth, who may or may not have killed her son Henry, finds herself on trial but liberated of a responsibility she increasingly resented. Teresa, nicknamed Mother Teresa for her squeaky clean image, wishes the trial would last longer because it gives her time away from her daughter. And Pak, the owner of the HBOT tank and a “goose father” – a South Korean phenomenon where patriarchs send their children and wives abroad while they save money to migrate as well. He feels “the shame of becoming less proficient, less adult, than his own child”, Mary, a teenager who serves as the family translator and is increasingly contemptuous of both her parents.

A migrant is like a really close friend who loves you, but can also tell you what you need to hear ... we bring that perspective

Kim’s father was neither a goose nor a penguin father (the latter being those who can’t afford a short annual visit like the former). The family left Seoul together for suburban Baltimore when Kim was 11. In Korea, a teacher had asked for students to nominate themselves to be class president; Kim was the only girl to raise her hand and the teacher slapped her with a ruler in front of the class, “for daring to think girls can be president of anything. Korea is a very male-dominated, patriarchal culture where having sons is everything. When my mum heard she was so angry and I think it was a big motivator for the move. Ironically, Korea had a female president before the US.”

When they arrived, Kim lived with her aunt and uncle while her parents ran a grocery store downtown, where they also slept, among the cans and food in the back room. Kim, an only child, resented their sacrifice. For the first time, she had her own bedroom and indoor plumbing – but no parents. “I accused them of abandoning me. We were so poor in Korea, so coming to the US was a fortunate thing. But losing contact with my parents was something I really resented, so I acted up.” It wasn’t until 40 years later, writing Miracle Creek, that she acknowledged it was a sacrifice: “You’d think after law school and having children of my own that I would have let it go. But we never talked about it. Writing made me consider what it had been like for them. I realised I had been a brat. They have read it and we had a really cathartic conversation. That’s the best thing that came out of this novel for me.”

Facebook Twitter Pinterest ‘I felt really sorry for us until I met these families, who were so upbeat’ … Angie Kim. Photograph: Tim Coburn

Before having her own children, Kim worked as a trial lawyer. She loved the drama but hated the machismo of the courtroom. After a busy period, she took a brief break in San Francisco; she went to an empty cliffside restaurant and spent the entire day there, alone with a bottle of wine and a plate of cheese and reading Tim O’Brien’s In the Lake of the Woods cover to cover. “When I closed it, I couldn’t remember being so happy. That day, I decided to quit.” Though she would later become a dotcom entrepreneur, then stay at home for her sons for a decade, she decided to be an author that day.

Decades on, with her first book under her belt, she finds herself alongside fellow migrant authors including Ocean Vuong and Viet Thanh Nguyen, writing back to the US about itself in both fiction and reality: all three recently signed a starry open letter calling for an end to inhumane conditions in detention centres on the US-Mexico border.

The migrant perspective is crucial in the US, Kim says, because “we are like a really close friend who loves you, but can also tell you what you need to hear. Migrants have a responsibility as people who have chosen to come to this country to bring that perspective, to make us stronger. I disagree with the argument that says we should be grateful, or shut up and ‘go back to where we came from’.”

As for Trump’s recent racist comments, she remembers a confusing two-month period when she first arrived in the US during which she was finally able understand enough English to know other children were mocking her, her looks, her smell, but without the language to respond. “I went from feeling grateful I could finally understand to feeling awful because these seemingly nice kids had been making fun of me the entire time. When I hear Trump saying, ‘go back to where you came from’, it takes me back 40 years. I’m fluent, I’m successful, I went to great schools. And all of those things, just hearing that happen to someone else, makes me cry and makes me feel like I don’t belong, even today.”

• Miracle Creek by Angie Kim (Hodder & Stoughton, £16.99). To order a copy go to guardianbookshop.com. Free UK p&p on all online orders over £15.