IT is a dreich morning as crime author Denise Mina cycles onto Glasgow Green. Wrapped up against the rain and biting wind, she glides to a graceful stop by the McLennan Arch overlooking the Saltmarket where we've arranged to meet.

Across the road stands a majestic Doric-columned blonde sandstone courthouse. It is here that our journey begins. Conversely, it is also where the storyline in Mina's latest novel, The Long Drop, reaches its dramatic, high-octane climax.

The gripping narrative centres on real-life serial killer Peter Manuel whose two-year murder spree claimed at least eight lives between 1956 and 1958. Dubbed "the Beast of Birkenshaw" after the housing estate where he lived, Manuel's name still sends a chill through close-knit Lanarkshire communities some 60 years later.

During his trial in 1958, thousands lined the pavements outside the court, erupting in jubilant celebration as Manuel was sentenced to hang for his heinous crimes, the third-to-last person in Scotland to be executed by capital punishment.

Today, the streets are quiet save for a few cars splashing through the puddles or the occasional person scuttling past, head bowed against the inclement weather.

Glasgow-based Mina has published 12 previous novels including the Garnethill trilogy, Paddy Meehan and Alex Morrow series. The Long Drop sees her move from the world of fiction to true crime.

Her hazel green eyes sparkle as she recounts listening to a podcast about the Amityville Horror while pedalling to our rendezvous. The Peter Manuel story is no less packed with macabre detail, but interestingly in tackling it, Mina has taken a fresh approach.

Rather than the grisly murders themselves, The Long Drop focuses on a meeting between Manuel and William Watt, a man whose wife, daughter and sister-in-law were shot dead at their home in Burnside, Rutherglen, on September 17, 1956.

Watt was arrested and held on remand in Barlinnie Prison for 67 days before the case against him was dropped. Manuel claimed he could get hold of the gun used to kill Watt's family. On a December night in 1957, Watt met Manuel to find out what he knew.

According to Mina, the pair spent 12 hours together, drinking, talking and criss-crossing the city in what she dubs "a grand tour of 1950s Glasgow". She first heard about the encounter as a throwaway line in a true crime book. Her interest was instantly piqued.

"I wondered: 'What happened there?'" says Mina. "I began investigating and piecing their night together to try and work out all the places they went."

Adding to the intrigue was the fact that Manuel – having sacked his lawyers and conducting his own defence – would later call Watt as a witness during the murder trial and asked him a series of questions about that night.

The pair's movements as they travelled around Glasgow that December evening are recorded in court transcripts. Mina used her steel-trap imagination to fill in the blanks, retracing Manuel and Watt's steps and the likely haunts they visited.

"Most of the places where it happened aren't there any more," she says. "As I cycled around, seeing the different locations, I could feel the city growing up around me."

Those locations include the former Jackson's Bar on Crown Street, a short hop across the Clyde from where we're standing. The pub itself is long gone, flattened along with the rest of the Gorbals as late 20th-century urban regeneration swept away the former slums.

Crown Street no longer runs in seamless entirety, its raft of new build flats, shops, cafes, tanning salons and hairdressers unrecognisable from the one Manuel and Watt would have walked.

Just around the corner is Florence Street, once home to Samuel "Dandy" McKay, a leading figure of the Glasgow underworld. Be it stolen cars or illegal guns, says Mina, all roads inevitably led back to here.

"There is only a spur left of Florence Street so I had to find friends who grew up there to ask them what it was like," she says. "It was really high, with perfect sight lines all the way down."

From the Gorbals, we recross the river towards the Merchant City. The Steps Bar on Glassford Street – which Manuel and Watt visit in Mina's book – is a perfectly preserved pocket of a bygone Glasgow, its wood-panelled interior a mock-up of the Queen Mary and dating back to 1938.

Unfortunately, we're too early and the shutters are still pulled down. Never mind, says Mina, let's head over to Gordon Street. It was here that the infamous Gordon Club – owned by Dandy McKay – lurked above what is now Greaves Sports and Pret A Manger.

The building has a gothic-looking entrance with a black front door which swings open to admit a delivery man, giving us a fleeting glimpse of the steep staircase to the upper floors – the same set of steps that Manuel tumbles down in Mina's book.

"The Gordon Club is where people met: journalists, police officers, councillors, lawyers and gangsters," she says. "It was quite a swanky club apparently."

When writing The Long Drop, Mina had a 1956 map of Glasgow pinned on the wall above her desk. It is this incarnation of the city – with its soot-blackened buildings and lingering sense of menace – that she conjures in the mind's eye while wandering through the streets.

Back at The Steps Bar, which has now opened, we take a pew in the snug area away from the main hubbub. Mina, 50, clearly feels at home in this quaint time capsule. It has echoes of an era that the Govan-born author, although slightly too young to remember, evidently feels a strong connection to.

The Long Drop is in part a love story to the Glasgow of the 1950s which Mina says began to disappear almost immediately afterwards. "Glasgow was so ashamed of itself then," she says. "It just wiped itself out. It is only now that people are beginning to realise: 'God, it was actually quite beautiful.' All the black buildings and how threatening the city felt – it was so noir."

Mina has a canny knack for talking to people. They open up in her presence like flowers craning towards the sun. "My sister is the exact same," she smiles. "She can talk to anybody. We are interested in people."

It is a skill honed during Mina's childhood where her father's job as an oil engineer saw the family move 21 times before she turned 17. "We were in Norway, Paris – twice – The Hague, Rotterdam, London, Invergordon, all over Europe – that whole oil family circuit.

"Because we moved so often we were always getting to know somewhere new. My mum and dad used to say,

'Wherever you live, you should treat it as if you are a tourist.' I think that inquisitiveness is a real gift."

Mina describes herself as having been "quite an odd wee person" as a youngster. "Some kids you meet and they're like an old person in a young person's body – that was what I was like. I didn't take any of it very seriously and just wanted to have a laugh with my pals.

"I was always in trouble and couldn't read for a long time – I just wasn't that interested. School felt like a holding cell. I was out of there like a rat from a trap."

Mina didn't harbour childhood ambitions of being an author. "I wanted to be a missionary, a nun, a film star and a nurse," she says. "I don't know what I thought I would do. I only thought about being a writer when I was 19 and started reading."

After leaving school at 16, she variously worked in a kitchen, bar, meat factory and care home for the elderly before studying law and publishing her first book in 1998.

Mina laughs when I ask whether she imagined having such longevity in her writing career. "I cannot believe I'm getting away with it, I really can't," she says. "I see better writers coming up and falling by the wayside, I see people being sucked into academia. I feel incredibly lucky."

As well as a skilled raconteur, she is an astute listener. "People in Glasgow are so generous with their stories," says Mina. "If you sit at a bus stop and chat to someone, they will tell you about their lives. And if you say 'Peter Manuel' to anyone over 50, they have a story to share."

Mina's own interest in Manuel first took root some years ago, when she met a woman in a church cafe who was doing a tour of the murder sites. "She asked if I had heard about Peter Manuel and started telling me about him. I found it such an amazing story.

"It is also a very Glasgow story because there is the official version and then there is the version that people tell each other. The official version doesn't make any sense. The story that people tell each other makes a lot more sense."

In 2013, Mina wrote Peter Manuel: Meet Me which was shown as part of A Play, A Pie and A Pint at Oranmor in Glasgow. "People stopped me at the back of the hall afterwards," she recalls. "I had William Watt as an innocent but all the pensioners, who knew the oral story, told me: 'You've got that wrong: it is much more complicated than that.'"

Mina began to delve deeper. "I think this is where conspiracy theories come from," she muses. "You read the official story and it doesn't make sense. People have a really strong sense of narrative, particularly in Glasgow. That whole generation is dying out and the oral tradition of the story dies with them. What does that leave? This nonsensical story that is the official version."

It is a theme she explores in the book, tapping into the lingering suspicions woven into Glaswegian folklore about Watt's true motives for meeting Manuel that night. While portrayed as a grieving husband and father valiantly trying to clear his name, there is a crackling undercurrent throughout that Watt perhaps knows more than he is letting on.

"William Watt comes across as not very believable," says Mina. "But then real people aren't always believable, are they? It is only on TV shows that everyone who is innocent is believable. Sometimes people don't have social skills, they are peculiar or pompous. There can be something odd about a person, but that doesn't mean they are guilty of a crime or murder."

Although, she later adds: "I think Watt went to meet Manuel because he was so caught up in the performance of an innocent man."

Equally, Mina believes there is more to the Peter Manuel story, suggesting that his behaviour may have been shaped by sexual abuse at a young age. "When he was 12, he stole from a collection plate in a church which for a Catholic boy is a big deal," she says. "It says something about his relationship with the church."

Manuel was sent to the same young offenders' institution as Irish writer Brendan Behan, who later alluded to predatory sexual behaviour amongst inmates in his book Borstal Boy. "Peter Manuel came out of there as a rapist and a murderer," says Mina. "It doesn't justify anything he did, but it is only in this generation that we can start to understand what might have happened."

It touches on a wider issue for Mina, not least challenging the belief that all serial killers are born evil. "I think we need to ask: why do we keep telling ourselves this same story?" she says. "What does it say about us that we want to believe that these things happen in isolation and have nothing to do with the fact he was in a borstal from the age of 12?

"It is another aspect of refusing to accept that sexual abuse happens. Or refusing to be compassionate to male offenders. If it was a woman, we would try and understand why."

Mina cites the example of US serial killer Aileen Wuornos. Severely abused as a child and having worked in prostitution since her teens, the abject horror of Wuornos's life culminated in the killing of seven men in Florida between 1989 and 1990. She was executed by lethal injection in 2002.

"Aileen Wuornos is interesting because people try to understand why she did it. She is one step away from people completely trying to understand because she wasn't heterosexual. If she was heterosexual and had children, people would be falling over themselves to understand.

"Then you get to heterosexual men and no-one gives a f*** about them and people don't want to try and understand. If we understand, we might be able to do something about it. But if we refuse to understand, we can just bang them up forever or hang them."

These are strong words, although Mina's shrewd analysis shouldn't be mistaken for misplaced sympathies. "Serial killers are real a*******," she says bluntly. "Psychopaths are a*******."

She is keen to hold a mirror up to what the serial killer story reveals about us as an audience. "No-one really acknowledged there was such a thing as serial killers until about the 1980s," says Mina. "It is a very new story, the serial killer as the outsider who does unbelievably bad things.

"People write about them as is they're a different breed or born evil. But actually, when you look at it, there are other ways these stories could go.

"Manuel is very obviously a psychopath and he lies to suit himself. He doesn't even try to be consistent in his lies because he doesn't really care what you think about him. That is Donald Trump. It can make you very successful in business.

"He is making things up but it is not problematic in his life – he has done well out of that behaviour. You could say that is normal criminality or it is a normal CEO behaviour."

Trump – who Mina describes as "needy, predictable – just a f****** a*******" – is a subject that regularly makes her blood boil. "I'm only listening to Magic Soul these days because I can't listen to Radio 4 any more," she chuckles. "It is Otis Redding on a non-stop loop and I'm still angry."

Mina is married with two children and lives in Glasgow. Fiercely private, the only time she clams up is when asked about this aspect of her life.

What she does cheerily divulge is that her favourite pastimes include "going to the pictures, travelling around, eating, not cooking – and I don't mean fancy eating, I mean sausage rolls – reading and listening to true crime podcasts".

Mina's next book is inspired by a self-described obsession with podcasts such as Making A Murderer and Serial. "There is a strong response that all those podcasts evoke in listeners which is thinking we know the truth," she says. "But, in fact, you are being manipulated by the storyteller.

"I'm writing about someone who is listening to a story and does what all of us want to do: drops everything in her life and goes off to try and solve the crime. It turns out she has done something awful in her own life and is running away from all sorts of things."

Mina writes about often brutal subject matter, but is clearly fascinated and cares deeply for the human condition. She taught criminology while studying for her PhD in the 1990s, but fervently shakes her head when I suggest she might have made a good police detective.

"No," she says immediately. "I'm too ambivalent. I can see both sides. I can't take a strong position because I always understand the other side – even if I don't agree with it."

The Long Drop by Denise Mina is published by Harvill Secker, £12.99. The author will be speaking at Aye Write! Glasgow's Book Festival on March 12. The Herald and Sunday Herald are the festival's media partners