With her debut novel The Girl in the Mirror, New Zealand author Rose Carlyle has doubled the trouble, introducing identical twins Summer and Iris, and placed them in the middle of a twisty, addictive thriller that has set the publishing world on fire.

There were bidding wars in the United States and Great Britain for the international rights, it's been translated into four other languages and a major movie deal has already been signed.

"It's been a bit surreal," says Carlyle, "I feel like a bit of an imposter."

Which is kind of what the book is about. It's impossible to describe the plot without giving too much away, indeed it's the kind of book where you don't want to. Suffice to say it's about taking an opportunity to live a life you've always wanted. When Summer calls Iris to Thailand to help her sail the family yacht to the Seychelles, both women are presented with a chance to change their lives. Throw in a multi-million-dollar inheritance, a fair bit of sex and a boat full of secrets and hop aboard.

Carlyle's taken some of her own chances. Single, 47, and the mother of three teenage children, she gave up teaching law in June to focus on writing full time. The second book is just about complete.

"It did feel for a while like the writing was the only part of my life that was for me," she says. "I was single, I had four teenagers, our nephew was living with us as well, I had gone and got a job and was adjusting to being back in the workforce after being a stay-at-home mum and life was very, very busy and it was hard work but it was this beautiful little escape."

For as much as the book is about sibling rivalry, Carlyle credits her older sister Maddie for much of the book's inception. Both sisters were writing and were comparing notes one day "and it was like we had half a story each".

"It was like the story chose us," she says. "There's this idea that stories are floating around in the sky and you have to reach up and grab them, it felt like my sister and I were together and at the same time we grabbed half a story and when we put it together we just thought we had to write this ... I know that sounds ridiculous but that's how it felt ... every stage of the book was a collaboration."

She said she's been asked several times if the book is based on her relationship with Maddie.

"Definitely not," she says. "We used to laugh about the absolute contrasts in the way Iris feels about Summer and the way we feel about each other. I know which sister I would rather have."

A crucial part of the book is set at sea aboard the sisters' family boat. Carlyle says this is the only aspect of the book Maddie wasn't happy with.

"She thought that books about people being lost at sea had been done quite a lot and I agreed with her but I said I have to draw on my experience ... I don't have time to go off and research something, I'm trying to raise a family here and keep my day job so I have to write about something I'd actually done in order to have that authentic feeling."

In 2013 Carlyle and her then husband packed up their house in New Zealand, bought a 62-foot sloop and sailed across the Indian Ocean to South Africa with the children on board.

"It was quite a special time," she says. "It's always busy with kids, it's no different if you're living in suburbia or living on a boat, the difficult part when you're sailing is that someone has to be up at all times, that can be exhausting, but it's great being there for your kids ... you spend a lot of time together and you really get to know each other and get along. It's like lockdown but without the daily walk."

If there's one thing the past few years have taught her it's that she's learned to have faith in herself.

"I've learned to have courage in so many ways," she says. "When it comes to writing it's quite difficult to hit send on that email when you're at the point of sending your manuscript off to a publisher, you could quite easily keep it for a long time thinking it's not quite right because it's never going to be perfect. But if you don't do it, it's never going to happen. It's about having faith in yourself and trusting your own judgement."