WALKING through New York's subway, the teenage Lin Anderson was pleasantly surprised when a stranger offered to help her down the stairs with her suitcase.
She accepted his kind offer. But what happened next shocked the stranger more than it did Lin. "He took off with the case, thinking I'd just stand by and let him get away with it. But I chased him up and down the escalators and screamed at him to hand it back.
"The superintendent who ran to the scene said all he could hear was this raucous Scottish voice he could barely understand!"
Four decades later Lin, now 57, still tackles criminals, but today she does it with a pen. Working from her Merchiston home, where she lives with computer salesman husband John, Lin weaves the tales of forensic scientist Dr Rhona MacLeod, whose experiences seem to get more disturbing by the book. Lin's cheery disposition conceals a dark mind from which bloody thoughts spill on to the page. Her fifth book, Easy Kill, is published on Thursday. This time round she sends her heroine to tackle a serial killer murdering Glasgow prostitutes. Its predecessor, Dark Flight, delved into an underworld of abduction, voodoo, female genital mutilation and castration.
More disturbing still, her stories are based on real events. "A lot of the material in the latest book was inspired by the prostitute murders in Glasgow in the nineties. Then just after I finished the book the Ipswich murders started happening. I was fascinated by the way the newspapers referred to them as women first, and then prostitutes. That's the message I wanted to get across with Easy Kill."
For Lin, the influence of a real-life case and accurate forensic science are the keys to creating the perfect crime story. She began to take an interest in cases dealing with DNA in the nineties – before forensics became "fashionable" through shows such as CSI. Eager to make sure all of the scenarios in her books were realistic, she even took a year-long forensic medical science course at Glasgow University.
"My lecturer there has become a main source of information for me. If I get an idea I will e-mail her and see if it is possible. For example, this book has a lot to do with the River Clyde, so I wanted to know if a particular type of seaweed would be found in there. If something can't be real there's no point in having it in the book.
"In Dark Flight I looked at the case of 'Adam', the unidentified torso found in the Thames. Nobody knows who he is but for the first time ever bone analysis traced him back to his origins in Nigeria. I found it fascinating that science could go that far. Real-life developments make better reading than anything I could make up."
Despite her love of all things forensic, Lin's writing style is anything but scientific. Rather than meticulously planning the plot from the first page, she admits that she doesn't have a clue where a story is going until the very finish. "I'll get an opening scene in my head and if it bugs me enough I know a story can be made from it. Although I never know exactly where I'm going next. It's not a tactic favoured by many writers, but I find it usually works out in the end. Although I admit I was a bit worried with Dark Flight. I had to write two endings."
Originally based on a pupil she taught when she was a maths teacher in the Highlands, Lin – who also taught at George Watson's – has now developed Dr Rhona MacLeod so much that she admits to feeling like she shares her life.
"I suppose it is a bit Jekyll and Hyde. I find myself dividing my time between my own personal thoughts and thinking about how an entirely fictional character would think and act in a given situation. To me –and some of my readers – Rhona is real now. If I'm thinking of a storyline I'll talk through it out loud and think 'What would Rhona do?'."
It is no secret that Rhona MacLeod's mentor and colleague DI Bill Wilson is loosely based on Lin's father, a detective inspector in Greenock, where Lin grew up. Lin suspects she might have inherited his nose for solving crime but says her own childhood was never intertwined with the workings of the criminal underworld.
"Back then things weren't openly discussed like they are now. People had never heard of child abuse. But my father used to give my sister and I coded warnings. One day he told us that if a man offered us a bottle of lemonade we were never to take it. We later found out that a man was going around our neighbourhood spiking lemonade to poison children."
In those days there were few places for women in the police, and it appears the same attitude often holds in crime writing today. Lin says detective novels filled with gore are often considered to be "boys books" that no woman could write.
"My editor gave his mum one of my books. She said she enjoyed it but that she hoped that the woman who wrote it was a nice woman. You wouldn't ask that about Ian Rankin," smiles the mother of three grown-up children.
"People presume women aren't suited to this type of writing, but females are just as capable, if not more so. Women tend to write in psychological ways and explore the darker side of human nature. If you read Val McDermid you'll find an excellent exploration of the human psyche. That can be a lot scarier than raw action."
So does the ability to conjure up such dark material indicate that Lin and her co-crime writers have sick minds? "Not at all," she laughs. "In fact my editor says crime writers have a reputation for being nice people, whereas romantic novelists are renowned for being grumpy. Maybe we get all of our badness out of the way through our books."