Seven years ago, Louise Ross swapped her career in financial law for a life of crime (writing). After a fruitless search for the traditional model of agents and publishers, she decided instead to do it all herself, selling more than seven million copies in the process.

Since 2015, Louise has written 18 books in the DCI Ryan series, four novels chronicling the exploits of forensic psychologist Dr. Alexander Gregory, a short story anthology, and the Cornish cove crime thriller. For the previous 10 years, she had been a financial services lawyer in London which involved tackling white-collar criminals and “trying to stop people perpetuating fraud”.

She said in an interview with the BBC that “I found after a few years I was not loving it and I could not say my heart was fully in it.”

Deciding to take a sabbatical, Louise, who by this time was married to a barrister called James, set her sights on studying forensic psychology.

But her work-break soon became a “lovely surprise” maternity leave as she discovered she was pregnant with the couple’s first child.

At around the same time, the couple were on a train bound for Edinburgh when, travelling up the Northumberland coast, she had a flash of an idea that went on to change her life.

“It was miserable weather but so atmospheric and I remember looking at the island and thinking it would be a great place to set a story. “I suppose tentatively I did always want to be a writer; my mum has found books I wrote when I was a kid.

“I was a big reader, I loved books, but it was always a giant leap to think you could go from being a reader to a writer.”

With the time offered by her sabbatical and the germs of a story, Louise decided to write a book.

Inspired by her love of the “golden age of crime writing” encapsulated by the likes of Agatha Christie, as well as her childhood passion for the good versus evil narratives of the Christopher Reeve Superman films and Star Wars saga, Louise found herself creating a new detective – Det Ch Insp Maxwell Finlay-Ryan.

His first adventure is on Holy Island, where he has gone to recover from his own recent trauma when he is confronted by the gruesome murder of a young woman whose remains are found in the priory ruins. Louise spent 18 months writing it around getting to grips with motherhood, before starting the hunt for an agent and publisher.

She sent it to 12 or 14 agents and publishers thinking that would be enough.

“I did have one offer from what I would call a midsize publishing house which was exciting, but when the contract came through and I was supposed to feel elated, I just didn’t.

“I thought, ‘I’m handing over an awful lot here, my intellectual property in perpetuity”.

Unsure what to do, Louise’s husband suggested she look at publishing her book herself through an Amazon-owned service called Kindle Direct Publishing.

“I didn’t know anything about it, I thought it was just vanity publishing, but it actually meant I could be in charge of my book and what happened to it.

Holy Island was published as an e-book on 1 January 2015 and sold 25 copies, all to family and friends, while Louise also printed a few copies to sell in local bookshops.

But by May it was number one in the Kindle store, knocking Paula Hawkins’ Girl On A Train, off top spot, with daily sales of about 4,500 for which Louise credits “word of mouth”.

Amazon’s algorithms also helped, with the more copies sold resulting in better promotion and more copies selling. The majority of her seven million-plus sales have been e-books although printed copies produced by Dark Skies Publishing, the firm run by her and her husband, can be found in mainstream and independent bookshops with audiobooks also available.

In November Dark Skies Publishing will publish its first book not written solely by Louise – an anthology from more than 50 authors to raise money for the UK homelessness charity Shelter.