BOARDWALK EMPIRE BY Nelson Johnson Ebury Press, 312pp, £16.99

Looking for two words to sum up Atlantic City, New Jersey? They'd have to be "sea" and "sin," especially when describing its heyday in the first half of the 20th century. Not only were normal rules of decorum suspended, even Federal law didn't take hold: Prohibition never happened there. The economy was dependent on tourism, so the city pandered to visitors, and as one long-time resident said: "If the people who came to town had wanted Bible readings, we'd have given 'em that. But nobody ever asked for Bible readings. They wanted booze, broads, and gambling, so that's what we gave 'em."

As a lawyer for Atlantic City's planning board in the 1980s, when applications for many of the casinos were being approved, Nelson Johnson - now a Superior Court Judge - grew fascinated by the resort's complicated history. He spent 20 years fact-finding and interviewing eye-witnesses, a task he describes as "a race against death". Many key sources were elderly and initially reticent. He was persistent, and the pay-off, Boardwalk Empire, benefits from the wealth of detail he unearthed or scrupulously verified. Johnson moves with a reasonable degree of grace between novelistic scenes and straightforward factual reportage. Many of these facts are so eye-popping that they require no further embellishment.

Atlantic City attracted extreme behaviour, which is surely what inspired HBO to commission an eponymous series - airing on SKY Atlantic HD in February - based on part of Johnson's book. No money or effort was spared. Martin Scorsese directed the pilot, the writer comes from The Sopranos, and among the stars are Steve Buscemi and Scotland's own Kelly Macdonald. But don't confuse the mediums. Johnson's expertise and interests - politics and the law - inform the book, making this a very particular history, and sometimes a bit dry. There are only brief mentions of things we identify with the seaside city, such as the Miss America Contest, and the performers - Sinatra, Martin and Lewis - who found fame in Skinny D'Amato's 500 Club.

Atlantic City was the brainchild of country doctor Jonathan Pitney, who dreamed of making his fortune outside of medicine. Originally known as "Further Island", and a camp ground for Native Americans, Atlantic City was beautiful, but insect infested. Nevertheless, from the mid-19th century, Pitney campaigned to transform it into a health spa for wealthy travellers.

Key to this was establishing a rail link to Philadelphia, Pennsylvania, the nearest city, where people went to "handle important matters". But despite the famous Mainline society scene, it was also a bustling factory town. So when the resort took off, it did not become a Mecca for the wealthy, but for hordes of blue collar workers keen for a day away from machines and urban grime.This huge influx created a demand for cooks, bottle washers, maids, and so on, and Johnson argues that Atlantic City owes its continued existence to the African-American community. Many of them were newly freed slaves, and even before the First World War, Atlantic City was "the most 'Black' city in the North". But this didn't translate into social mobility. "As Blacks grew in numbers, the racial attitude of Atlantic City's Whites hardened."

The Republican Party dominated Atlantic City for the first 70 years of the 20th century, but the resort was ruled by a partnership of politicians and racketeers who were virtually indistinguishable. One of the most colourful was Enoch "Nucky" Johnson, whose reign lasted 30 years, reaching its acme during Prohibition. A large and imposing man with a penchant for lavender and chocolate suits, he spent hours of every day dispensing alms to the city's poor from his bathchair.

Johnson (no relation to the author), like Louis "The Commodore" Kuehnle before him, ran Atlantic City as a patriarchy. If you were down on your luck, if your child was hungry, if you needed medicine or lacked funds to bury your husband, Nucky rode in like the cavalry and smoothed out all the bumps.

But the trouble with patriarchies is that you have to do what Daddy says. The mandatory payback for all this TLC was a strictly enforced system of tithing that ensured a steady stream of funds for the Republican Party. "In order to keep their jobs, city and county workers had to kick back from one to seven percent of their salary to the local Republican Party," writes Johnson. Even racketeers had to pay protection money, so there wasn't a whorehouse, gambling den or illegal saloon that wasn't in Nucky's debt.

So corrupt was the city that when Lucky Luciano, a mate of Nucky's, called the first ever convention of American mobsters, they didn't waste time debating where to meet, but had Nucky book them into Atlantic City's finest hotel. Business was conducted on the ocean-front. "Once they reached the sand, they took off their shoes and socks, rolled their pant legs up to their knees, and strolled along the water's edge discussing their business in complete privacy."

With the repeal of Prohibition, Atlantic City's fortunes waned. By the time of the 1964 Democratic Convention the place was a shambles, causing the politicians not a little embarrassment.

Johnson explains how this decline led to the introduction of legalised gambling, offering insights into the workings of Resorts International - which started out as a company that sold paint - and laying bare the debt Donald Trump owes to his father, Fred, for laying the foundations for his empire.

Anyone interested in the political and social history of New Jersey will find much to admire here, but I suspect there will be an even greater audience for the HBO series.

For as Dr Pitney discovered, and Nucky Johnson encouraged, there's just no dampening people's baser instincts.