It’s a Wednesday afternoon in Bala, in mountainous North Wales, near the glacial lake known to locals as Llyn Tegid, and British author Clare Mackintosh is at her 18th-century Georgian manor house, reflecting over Zoom on the pleasures of small-town living. “We have a high street, shops, and a supermarket, then not a lot more for an hour or so,” says Mackintosh, who impulsively moved from England to Wales in 2016 with her husband and three kids to start a new life and reconnect as a family. “If I walk out my front door, I’m in town, and if I walk out the back, I pass my chickens and my sheep; say hello to my goat, Pete, who’s quite the local celebrity; and then get to the lake across the fields. It’s wonderful. And Welsh is spoken everywhere.”

Lauded for her novels’ twisty plots and surprise endings, Mackintosh made her debut with the 2011 psychological thriller I Let You Go, about the hit-and-run of a five-year-old boy; her books have sold more than two million copies worldwide, according to her publisher, Sourcebooks Landmark, and have been translated into 40 languages.

Her latest, The Last Party, out in November, is the first installment in a crime series starring “spiky” Welsh detective Ffion Morgan, who teams up with an English detective to solve the murder of a developer of lakeside vacation homes.

“As soon as Ffion walked onto the page, I felt that she was someone who was going to be here for longer than one book,” Mackintosh says. “She’s the first character I’ve had who does stuff I hadn’t planned for her to do.”

Mackintosh got the idea for the novel—a Welsh-English cross-border murder investigation—while taking a wintry New Year’s Day plunge into Llyn Tegid with friends. “We were about to go in the water and it was beautiful,” she recalls. “The mist was lying on the water, the mountain was in the background, everyone was saying how stunning it was, and I was privately thinking, what if a body floated through the water right now?”

Crime has never been far from Mackintosh’s mind—before she was writing about it, she was fighting it as a police officer in England for 12 years. She joined the force “by accident” after walking into a recruitment lecture during her last year at university. “I must be suggestible, because I left with an application,” she says. “A lot of the crimes I dealt with weren’t exciting. Criminals can be stupid—they’re not Agatha Christie villains with twirly mustaches committing dastardly deeds. They’re a bit thick. What I learned was storytelling. As a police officer you’re dealing with unreliable narrators or talking to crime victims and trying to find out what happened. It was a good training ground for a writer.”

Mackintosh’s agent, Sheila Crowley at Curtis Brown, says, “Clare transports readers to the heart of her stories. You can feel the jeopardy. I know writers who just open their laptops and start writing. Clare’s a planner. The first time I met her she had flowcharts and spreadsheets explaining what she was going to do with each character, in each chapter. She’s super smart.”

Mackintosh’s editor, Shana Drehs, says that her ability to keep readers guessing makes her stand out in an increasingly competitive field. “Expectations for thrillers have gone way up in recent years,” Drehs notes. “Writers have to perform at an even higher level than they used to in order to get that same reaction from audiences, and Clare manages to do that. She executes her twists flawlessly. It’s brilliant.”

Born near Oxford in 1978, Mackintosh says she “read constantly under the bedsheets with a torch” as a kid, sometimes working through two books in a day, and as a teen wrote stories and bad poetry (“as one does”). In 2008, she gave birth to twins, one of whom, a son named Alex, suffered from brain damage and died at five weeks old.

“I often wonder if I would’ve been a writer if my son hadn’t died,” Mackintosh says. “It unlocked something in me and made me less careful about what people thought, or whether it went well or didn’t, because nothing mattered. The worst possible thing had happened and it made me more reckless. I don’t think I would’ve left the police if Alex hadn’t died. So many things are predicated on that terrible loss.”

Mackintosh shares her life with her loyal readers in online posts—she’s talked about her grief and postpartum depression—and estimates that she spends 20% of her working life writing and the rest on social media and other forms of reader engagement. She runs a popular Facebook book club, sets up meet and greets across the U.K., and sends out newsletters.

“It feels disingenuous to have someone else engaging with readers when they think it’s me,” Mackintosh says. “I ask myself, if I didn’t do social media and wasn’t thinking of ideas to promote books, would it make a difference? I don’t know. Am I willing to risk it? Probably not.”

The author has also made it her mission to visit every bookshop in Wales. “I haven’t managed it yet, but I will,” she says. “I want to speak to people and say thank you—personal relationships make a difference.”

Fellow British crime writer Ruth Ware, a friend and author of the bestseller The It Girl, praises Mackintosh for her keen eye and authentic voice. “As a writer, when you like someone else’s book, you’re either supposed to love them or hate them because you think, I wish I’d written that,” Ware says. “Clare and I clicked. As a former police officer, she brings an authenticity to her work that’s hard to fake. We’re women writers working in similar genres. We should be rivals, but we’re friends. Crime writers are lovely people. It’s a nice community to be a part of, and Clare epitomizes that.”

Mackintosh hopes to alternate between writing standalone books and her DC Morgan series. “I don’t know where Ffion will be in five years, and that’s exciting,” she says.

The Last Party was optioned by 5 Acts Productions after a bidding war (“It was a very sought-after title,” says film agent Camilla Young) and is being developed for BBC television, and Mackintosh is at work on book two, as well as a nonfiction book about grief. Her move to North Wales is a reminder that the universe is full of opportunities for new beginnings.

“What’s great about life is that you can reinvent yourself,” she muses. “I hate when people feel stuck in a box, either in a relationship or a job. There’s always another life waiting for you.”

Elaine Szewczyk’s writing has appeared in McSweeney’s and other publications. She’s the author of the novel I’m with Stupid.