ON HER first visit to Barlinnie, Helen FitzGerald recalls, she felt “absolutely terrified”.

“I remember walking past a group of men, serious offenders, who were on their way to start work for the day, and they were surrounded by guards,” she says.

“It all seemed so inhumane, so weird and otherworldly. Looking back, what surprises me is how quickly I became institutionalised. After day three, it just felt normal.”

Helen’s experiences as a criminal justice social worker in both the prison and working in the community in Paisley, have made it into her book Worst Case Scenario, recently shortlisted for the prestigious Theakston Old Peculier Crime Novel of the Year award. The winner will be announced next month.

It is her second time on the list – the last time was for The Cry, a powerful thriller made into a hit TV drama starring Jenna Coleman.

“It has come out of the blue,” she smiles. “Both times I’ve been on the list have been for books I wrote when I was a bit fed up, when I was looking for a bit of fun.”

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She adds, with a laugh: “Not that The Cry was much fun, of course. But it was about doing something just for me.”

The Cry – about a couple facing intense media scrutiny after their baby son disappears – was a huge hit. Now it looks like Worst Case Scenario may also make it on to the screen, with a seven-way bidding war for the rights underway.

“I’m not allowed to say anything,” she apologises. “But fingers crossed it will happen.”

Worst Case Scenario is the story of Mary Shields, a moody, acerbic probation officer, dealing with some of Glasgow’s worst cases.

Into her world comes Liam Macdowall, imprisoned for life for the murder of his wife. He has published a book of letters to the dead woman, which have made him an unlikely hero and a poster boy for men’s rights activists.

When Liam is released on licence into Mary’s care, a chilling psychological battle ensues – and Mary will stop at nothing to unleash her own brand of justice.

“It’s the crim-iest crime novel I have ever written, I think,” says Helen, who has written a string of successful thrillers, including Viral, Dead Lovely and The Exit. “It’s set in a world I have dipped in and out of for most of my adult working life.

“I started writing because I was feeling burnt out – even though I was working part-time, it was still full on. It’s a hard job to do, the kind of job in which you don’t realise you are feeling burnt out until one day – whoompf, it happens. I was menopausal too, and full of anxiety about that.

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“I was about halfway through a book, and suddenly Mary walked in. She just jumped off the page, this angry woman who has lost her filter, a real loose cannon. So I abandoned the first book, and started writing about her.”

Mary has particularly struck a chord with women readers.

“It’s been great to hear from them,” says Helen. “Menopause is still not talked about very often. I was unwell for a couple of years, because of anxiety and depression brought on by the menopause, and talking about it made me realise I am not the only one - many women have told me they feel the same.”

Read more: Glasgow author explores every parent's worst nightmare in The Cry

Helen’s latest novel, Ash Mountain, was due to be released last month but because of COVID-19, will now be published in August.

“It’s about a small town in the lead up to a huge bush fire,” she explains. “It’s a bit of a departure but I’m really proud of it.”

Worst Case Scenario has had rave reviews, with many critics praising it as “laugh-out-loud funny”.

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“I hadn’t meant to be funny, that was kind of accidental,” says Helen. “But a lot of the people I worked with, clients and social workers, are very funny people and great storytellers. It’s what I miss most about the job – that camaraderie.

She adds: “It was really tough a lot of the time, but when you realised that you had helped, that you had stopped someone re-offending by providing the right support and tackling attitudes, that felt good.”