'This was the hardest book to write. I was tortured by it'

Yes, you read that right. Criminal justice social work. It's not the most obvious step to take if you're looking to charge your batteries, I'd have thought. Fitzgerald thinks otherwise.

"I like the job and the values of it and every day is fascinating," she tells me, her Australian accent still very apparent despite the fact that she's lived in Glasgow for more than 20 years now.

And what's the alternative, she says? "I was just me in an attic with my own head and my own ideas, talking about myself, thinking about myself. It's a recipe for alcoholism and craziness."

This morning in the CCA it's all coffee and good-humoured sanity. Across the way, Fitzgerald's husband Sergio Casci, himself a writer, and Fitzgerald's mum, over on holiday from Australia, are finishing their breakfasts. As they do so, Fitzgerald - mid-forties, sharp-featured, sharp-minded - is telling me about growing up in Australia, nearly dying in Nepal, her teenage children's reading habits (not great, it seems), and her days in Barlinnie.

If you read The Cry you can understand Fitzgerald might want to take a break from fiction. For all that it's a book you find yourself greedily gulping down, the subject matter is tough and painful. It begins on a plane trip from Scotland to Australia, a baby that won't stop crying and a mother, Joanna, who is struggling to deal with the fact. It quickly develops into a mother's worst nightmare. "This was the hardest book to write ever," Fitzgerald admits. "I was tortured by it. I hated writing it. I got into Joanna's head, much more than with any other character. I really felt what she was feeling."

It's also a book about trial by media and, very 21st-Century this, social media. The terror of Twitter. Even so, you can possibly see echoes of the Lindy Chamberlain case somewhere in the book's DNA. Chamberlain, whose baby Azaria was dragged away by a dingo in 1980, was convicted of cutting her nine-week-old daughter's throat. She was exonerated in 1987, but it was only last year a coroner confirmed that Azaria was killed by a dingo.

"That was the crime story I grew up with," Fitzgerald admits. "It was all anybody spoke about. I remember my Dad happened to be in Alice Springs when the trial was on and he went and came back and said 'she's guilty, she's so guilty.'"

This is one of the The Cry's disguised probe points. There's a light-touch feminism to it in the way it investigates how such cases often put the mother (less so the father - can you remember the first name of Lindy's husband?) in the dock of public opinion. "The woman always takes the blame," says Fitzgerald. "Even with the McCanns. It was all about Kate. 'What does she look like. Is she grieving properly?'"

Fitzgerald grew up in a small town called Kilmore on the edge of Melbourne, the 12th of 13 kids, in a house built by her engineer Dad. "It was quite a bizarre little town when I think of it. We had a jail in the town. There were stories Ned Kelly's father had escaped from there. Down the road there was a sale yard where all the cattle would be sold. An abattoir - we called it the bacon factory - across the road. We were probably the only Catholics in the street.

"It was quite divided between Catholicism and Protestantism. Even had separate cemeteries. I used to walk to school past the state school and they used to calls out "Catholic dags/dressed in rags/ eating ... what was it ... something out of bags'."

She was a sporty kid despite her asthma. Not much of a reader, but she shared her English teacher mother's love of poetry and language. But it was only when she met Sergio - or Serge as she calls him - years later that she seriously began to write. "I didn't try and start writing short stories until I met Serge." Their plan had been to become international writers together, spending six months in Glasgow and six months in Australia every year. "Then we had kids and that was totally screwed."

Maybe she was always going to leave home. "I remember being somewhere quite Australian and looking out over a flat brown lake with nothing much in it - swampland - and thinking 'I can't stay here. I've got to go."

She went. To Nepal, aged 23, where she nearly got lost in the Himalayas when she opted to follow a "big, hunky Australian guy" on a trek. It was when it started snowing - and it turned out the big hunky Australian guy had never seen snow before - that she started to worry. As the night closed in she was lucky there was a guy from Glasgow called John who pulled the group all together and took them over a summit and found a cabin to stay in.

She arrived in London with a one-way ticket and £50 in her pocket, got some cleaning work and started squatting in a business property that had gone bust. "A bit naughty, I suppose. We did leave as soon as they told us to. It was one huge fabulous party. People say 'I'm not going to London and live with Aussies. I'm going to explore the real London'. I loved living with Aussies in London, because they're all completely debauched and having fun and you never get that chance again in life ... except maybe with your midlife crisis. But then you hurt people."

She met John again in London. He would eventually introduce her to Casci. In the meantime she started working in a hostel for homeless ex-offenders. "I had a social conscience, I suppose." She toyed with the idea of social work but wasn't keen on working with children and families. But when she moved to Scotland - to Edinburgh originally - she got a job working in a unit for high risk offenders, many of them sex offenders, most of them male. "It was just me and seven high-risk offenders and it was a really scary job."

Even so, when she then moved to Glasgow she continued to dip in and out of social work. She worked in Barlinnie for two-and-a-half years and again didn't enjoy the experience. "I felt incarcerated too. I think most people do. I remember the first day the guys walking in all in the same clothes and it really upset me. The second day I was used to it. The loss of humanity ... I was also upset that no one whistled at me. 'Surely in prison.' Not one."

She works in the community in Paisley now. She much prefers that. "In prison there's very little you can do for people. They're just putting their heads down and doing the time. There's nothing at stake. Outside there's a lot at stake. You can really help them stay out."

But she remains a writer too. Why does she write? "Probably because I can't not. That's all I could say. I'm compelled to. I enjoy it."

She has already written another novel after The Cry. It's at the editing stage, her least favourite bit. But at least she has her most supportive critic to hand.

What's it like living in a house of writers? "It's fantastic mostly. He will read everything I need him to read.

"If I was living with a stupid writer it would be hellish, but luckily I'm living with a really clever one. The hard thing about it is we're together all the time so you don't have anything to say at the end of the day."

Her daughter Anna is 16 and her son Joe 13. They've yet to read their mother's books. Would Fitzgerald want them to? "I don't know. One day I hope they'll say 'oh that's what you were doing all those years'."

They're both great writers too, Fitzgerald says. But she's not sure that means they will necessarily follow in the family tradition. "They don't want a stupid job like that. They want one with a pension."

The Cry by Helen Fitzgerald is published by Faber & Faber, priced £7.99.