Sonchai and Calvino dwell in the Thai capital’s underbelly of bar girls, streetwalkers, ladyboys, drug dealers, hustlers, swindlers, hoodlums, drifters, pikers and low-lifes. They patronise the city’s red-light districts, where they deal with Russian gangsters, British ne’er-do-wells, Khmer tattoo artists, locals down on their luck, and cops on the take.

They aren’t the only hard-boiled sleuths plumbing the depths of Bangkok’s vices. Take Scott Sterling, a cash-strapped former CIA agent who likewise moonlights as a private eye in a shady netherworld of prostitutes, shifty expats and unceasing debauchery.

Then there is Bob Turtledove, an antiques dealer who goes up against gangsters, hitmen and thuggish Thai boxers. Eddie Dare, a downwardly mobile lawyer from San Francisco, is at it too, chasing a vast stash of stolen Vietnamese money in Bangkok.

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And that is just for starters. All these fictional characters are popular fixtures of Thailand’s crime mystery landscape, which boasts a ceaseless stream of titles by Bangkok-based foreign authors, primarily from Britain and the United States. In local English-language bookstores, entire shelves are devoted to the genre.

“Bangkok’s expat crime fiction scene is booming,” states CrimeReads, an international crime fiction website, calling the city “a capital of world noir”.

Many of the novels do more than just titillate. They have given Thailand’s boisterous capital a new alter ego, with its exotic aspects lovingly described and its sordid side greatly dramatised. The books often read like sights-and-sounds travelogues crafted onto whodunit mysteries featuring the city’s multicultural kaleidoscope – or caricatures of it.

“For a writer, life in the raw in Bangkok is gold,” says John Burdett, 69, an Englishman who has written a series of acclaimed novels featuring Detective Sonchai.

A Londoner who worked as a lawyer in Hong Kong before he retired in Thailand, Burdett has found a new calling as a novelist. Bangkok 8, his first book featuring Sonchai, became a runaway international bestseller when it was published in 2003, and was followed by five other novels.

“The variety of people living here is astonishing,” Burdett says. “And they all come together in this fascinating, dynamic place, which welcomes absolutely anyone who wants to do something legal – or even illegal. It’s a truly cosmopolitan city, like Hong Kong used to be.”

Not for him the well-off and the well-connected in whose circles he once moved. These days Burdett prefers the humbler world of Thai street vendors, motorcycle taxi drivers, masseuses and sex workers.

“Even when I was a pompous lawyer in Hong Kong, I never liked the attitudes of the wealthy Anglicised elite,” Burdett explains. “I always thought there was more truth and vitality to the lives of people who are struggling to earn a living.”

To do research for his books, the Englishman frequented working-class hang-outs around town to chat with locals in his passable Thai.

“You ask a stranger a question and they’ll give you a straight answer, which is very good for a writer,” he says.

Christopher G. Moore, 68, a former law professor from Vancouver, Canada, has found similar inspiration in Bangkok’s steamier side and its colourful cast of characters for his novels chronicling the adventures of Vincent Calvino, whom one reviewer called “the Thailand-based reincarnation of [American writer Dashiell Hammett’s] private eye Sam Spade”.

“Each investigation is a quest that is taking Vincent Calvino to a new area of exploration and discovery,” says Moore, who resigned from his tenured position at a Canadian university in 1984, turning his back on academia, whose atmosphere he found stultifying. He opted instead for exploring the world and writing about it.

“In books, you can pry open what lies beneath the surface,” he says. “That’s what private eyes are hired to do as well.”

Moore arrived in Thailand on a tourist visa in 1988 with a laptop, a small suitcase and a plan to stay for a few months. The months stretched into years, then decades, as he stayed put and turned into “the grandaddy of Bangkok novelists”, as an expat blogger calls him.

The city has changed greatly since Moore’s first Vincent Calvino novel was published in 1992. The nature of his protagonist’s investigations has morphed, too, as Calvino repeatedly got himself entangled in current affairs. The climate of political repression that ensued after the military coup in 2014 served as the backdrop for Moore’s 2015 novel, Crackdown.

“The series is a chronicle of technological, social and economic change in Thailand over 30 years through the eyes of a private eye. The books are like time-lapse photography over three decades, frame by frame,” Moore explains.

“In each book you want to explore larger themes while a private eye is trying to solve a particular case,” he adds. “The question is: what’s the subject of conversation at the time? What’s the inflection point of history at that moment?”

The Canadian author’s 17th novel featuring Calvino, Dance Me to the End of Time, published in January, is set in a dystopian Bangkok in the grip of apocalyptic environmental change.

That scenario is no mere flight of fancy. Built in a river delta’s marshy terrain upon soft clay, Bangkok is a flood-prone metropolis that lies only 1.5 metres (4.9 feet) above sea level. The weight of massive concrete structures has been causing the city to sink by up to 2cm (0.8 inches) a year.

Driven by climate change, rising sea levels could submerge parts of Bangkok within a few decades, experts say. The worst-affected will be the urban poor who already have it rough in teeming shantytowns alongside sewer-like canals.

For insights into the lives of the city’s have-nots, Moore used to hang out at busy fish markets early in the morning and spend time in the so-called Slaughterhouse, a large abattoir in a squalid inner-city slum notorious for poverty, crime and substance abuse.

“In the old days there were workers and illegal immigrants living in the rafters of these huge wooden structures, almost like bats in their nests,” Moore recalls. “You could hear the squealing of the hogs as they were being killed all night long.”

Social issues such as rampant corruption, weak law enforcement and official caprice are likewise grist to the mill of expat crime novelists. The same goes for the stark contrasts between rich and poor in a metropolis in one of the world’s most unequal nations where the top one per cent owns two-thirds of the wealth, according to investment bank Credit Suisse.

“With the Skytrain and all the pedestrian walkways up there, people can avoid being in the city almost altogether. They’re in the sky!” Moore observes. He means Bangkok’s elevated light-rail network and the raised skywalks that connect stations directly to fancy shopping malls, office towers and high-end condominiums.

But for Bangkok’s crime fiction writers like Burdett and Moore, the city’s real appeal lies at street level. That’s where a notorious red-light district with cigarette smoke-scented go-go bars employing the daughters of rice farmers can hide in plain sight down an alley among upscale hotels, condominiums and malls in a posh part of downtown.

“There are literally thousands of possible stories out there,” Moore says.

Bangkok’s crime fiction writers just have to keep looking for them.