In India, the Bengali writer Nirad Chaudhuri once quipped, even exceptions run into the millions. The message to anyone preparing to sit down to write a book about this diverse, dynamic, often discombobulating nation is clear: avoid stereotypes, embrace contradictions and, above all, keep a calculator close.

Nowhere is India’s mind-boggling, multi-zeroed exceptionalism more in evidence than in the growing ranks of its billionaires. At the last count, the members of the ten-figure plutocracy numbered 119, with one new arrival joining the club every month or so. Their combined worth: $440 billion. And this in a country where roughly three in every five people live on less than $3.10 per day.

Wisely, James Crabtree, the Financial Times’s former Mumbai bureau chief, keeps to Chaudhuri’s advice. In a book remarkably free of moral judgement, he delves into the world of India’s ‘Bollygarchs’ with the right mix of wide-eyed fascination and cool-headed analysis. The result is a pacey and perspicacious account of what Crabtree refers to as India’s ‘new gilded age’ – a phrase borrowed from Mark Twain’s description of late 19th-century America, where, as Crabtree recalls, everything ‘glittered on the surface … but was decaying underneath’.

The Billionaire Raj kicks off with the story of Mukesh Ambani. Worth more than $40 billion, according to Forbes, this son of a petrol-pump-attendant-turned-tycoon is India’s richest man. In 2005, he began building a 27-storey apartment block in the heart of Mumbai. Equipped with every imaginable luxury (indoor cinema, rooftop bar, six floors to house his car collection, space for six hundred domestic staff, twenty-five tonnes of imported chandeliers), the building was reputed to have set him back $1 billion.

Nor is Ambani the flashiest of India’s super-rich. That prize goes to Vijay Mallya, owner of the Kingfisher beer and airline brands – or it did before his recent fall from grace. At the height of his success, the self-branded ‘King of the Good Times’ owned a Formula One team, travelled the world in a private Boeing 727 and contracted music stars like Lionel Richie and Enrique Iglesias to sing at his birthday parties. Whither Gandhi and his warnings about the ‘monster god materialism’?

During his five years reporting in India, Crabtree has had occasion to cross paths with more than his fair share of India’s super-rich. They make for a colourful cast and one that he brings to life in a style that is consistently precise and observant. And so it is that we meet Gautam Adani, the Gujarati infrastructure and energy tycoon who always holidayed with his mother until her death, and Rakesh ‘Big Bull’ Jhunjhunwala, the boozy financier with a ‘millenarian faith in India’ and a bawdy sense of humour.

But this is not a book primarily about personalities. Crabtree is no Tatler hack or tabloid muckraker. Cheap credit lines and accountancy tricks, infrastructure financing and resource licensing: these are what work him up. It is testament to his skill as a writer and storyteller that the hard economics at the core of The Billionaire Raj neither bores nor overbears.

India’s billionaires are ultimately just the public faces of a story that goes much deeper. It is a tale that, like so much in this former jewel of the British Empire, has its roots in India’s independence. Viewing private enterprise as a vehicle of colonialism, India’s early leaders eschewed free-market economics for state-dominated socialism. The arrangement lasted until 1991, when India finally ditched its hopes of self-reliance and opened itself up to the world.

Liberalisation brought foreign investors flocking in and sent the stock markets soaring. What it didn’t do was sweep away the country’s reputation for graft. In the so-called ‘Licence Raj’ of the post-independence era, making big money depended on acquiring the right permissions from politicians. After 1991, capital began to flow more freely but the politicians did not disappear from the system. The result: an unprecedented coming together of private interest and public office that has given birth to stratospheric personal fortunes and a ‘new culture of bling’.

Crabtree’s in-depth description of India’s descent into crony capitalism doesn’t just take him into the boardrooms and private jets of the mega-wealthy. It puts him on the hunt of wheeler-dealer parliamentarians and potentate state ministers. India might be the largest democracy in the world, but it is also one of the most expensive. Campaign expenditure in the 2014 election is reputed to have reached $5 billion. Politicians are never free from the ‘money power’ of their private-sector backers.

If the book has a weakness, it is in the familiarity of some of its examples. The ‘grand wholesale corruption’ that suffuses the country is well known – especially to Indians. Crabtree’s discussions of such calculator-busting scams as the illicit issuance of hundreds of mining licences and the bargain-basement sale of 2G phone rights will be met with a weary shake of the head.

Crabtree’s unique achievement is to probe the peculiarities of Indian cronyism and lay out its structural causes. There is a fascinating section, for example, on India’s southern states, which, despite being ‘staggeringly corrupt’, still manage to deliver a modicum of development for their citizens. Why? Because the politicians take their cut and leave the rest of the cake. In the north, they just scoff the lot.

Today, India finds itself at a crossroads. BJP leader Narendra Modi won office four years ago on a promise to clean up politics. Backhanders continue, of course, but the worst scams seem to have stopped. In classic Financial Times editorial style, the conclusion provides a series of recommendations to end profit-sharing among India’s elite: it is an eminently sensible list that will, for that reason, almost certainly be ignored.

Whether Modi turns out to be a Theodore Roosevelt ushering in a Progressive Era of reform or a Vladimir Putin overseeing a ‘saffron-tinged’ oligarchy remains to be seen. Crabtree, naturally, hopes for the first, as most Indians surely must too. For sheer chutzpah, India’s billionaires provide tremendous value. All this makes for a thoroughly entertaining book, but also for a sadly enfeebled and unequal nation.