China, Jonathan Fenby argues in his new book, "does everything on a scale that breeds shock and awe". It has the largest monetary reserves in the world, at more than $3.2 trillion; it consumes more than a third of the world's supplies of key metals and half the world's cement. Every two and a half minutes, Greenpeace estimates, it produces enough toxic ash to fill one Olympic-size swimming pool. It is a nation of violent contrasts: it may have as many as 600 dollar billionaires, as well as 300 million people without access to clean drinking water. Despite the government's fixation on national unity (its "tiger head"), Fenby asserts, it is a mass of snake's tails. "There is not one China but a hundred, a thousand or a million."

The extremes that characterise China mean that it is a remarkably hard country to make sense of. The place is so large and diverse that you can dig up reasonable bodies of evidence to back up wildly diverging hypotheses about its future. In 2010, Robert Fogel, a Nobel prize-winning economist, predicted in Foreign Policy magazine that China would end America's global dominance in 2040. By this point, he proclaimed, "China will account for 40% of the world's GDP, dwarfing the US (14%) as the world's largest economy". His article was paired with one by Minxin Pei, a professional China-watcher who presented a more sober perspective. Pei argued that an ageing population, environmental degradation, inequality and corruption, and an opaque business culture threaten to bring the country low long before it comes anywhere near ruling the world.

Everyone agrees that China has grown extraordinarily, and relatively easily, over the past three decades. Consensus on what will come next is practically non-existent: perhaps the same rate of growth; or perhaps a massive demographic slowdown, an over-inflated economy, environmental meltdown and the strains of one-party rule will bring the whole edifice down.

As a handbook on the confusing state of contemporary China  covering the economic, political, social and historical essentials of the story  Tiger Head, Snake Tails succeeds admirably. Fenby moves between the expansion of transport and infrastructure that has unified the country logistically as never before, the cities that are spearheading the country's economic miracle, the poor working conditions and growing militancy of its labourers, its diverse mass of enormous factories and cottage industries, the push and pull between the centre and the provinces, between Han Chinese, and Tibetans and Muslims. He takes time out to glance at Hong Kong and Taiwan, both of which present intriguing Chinese alternatives to the mainland political paradigm.

One of the big questions hanging over China's future concerns the stability of its political system. Until now, analysts have observed, the government has struck a successful tacit bargain with its people: tolerate our authoritarian rule and we'll make you rich. Despite a phenomenal expansion of economic opportunity, political freedoms lag far behind. The Communist party is unflagging in its efforts to maintain its monopoly on power: "dissidence", Fenby writes, "is equivalent to treason." Liu Xiaobo, winner of the 2011 Nobel Peace prize, languishes in jail after petitioning the government for democratic reform. Human rights lawyers are tortured and crippled. A television talent show, Supergirl, that required viewers to vote for their favourite contestant, was cancelled, at least partly because of fears that audiences would become hooked on the idea of popular choice.

And yet beneath this rigid power structure, a barely controlled chaos often prevails. Corruption is rife, and chancers taking advantage of market reforms have generated scandal upon scandal: food safety, thefts of the national heritage, horrifying rail and road accidents. One of Fenby's most gripping chapters is on the "trust deficit" that clogs so much of life in China. In 2008, the country was rocked by revelations that one of its biggest baby-milk companies had been adulterating its formula with ground melamine (essentially, powdered worktop). Doctors are routinely bribed by patients anxious for preferential treatment; medicines are often counterfeit. The architects of a pyramid scheme made billions of yuan persuading gullible customers to buy "medicinal ants" that needed feeding with egg yolk and cake every three days. Political corruption is endemic. A couple of years ago, a six-year-old girl  when asked by a television interviewer what she wanted to be when she grew up  answered: "a corrupt official". One wealthy smuggler flourished for almost two decades by handing out ten million yuan a month in bribes to his high-level connections. As a result, China seethes with injustices and public discontent.

There is a risk that a book summarising such a monumental story might get bogged down in dry, statistical detail. Fenby avoids this through lively, first-person reportage and vivid vignettes. Throughout the book, he takes a serious-minded delight at the country's absurdities and grotesqueries: the local government that required female civil servants to have "symmetrical breasts"; the railway minister with 18 mistresses; the Daoist priest who won a wealthy following by sitting underwater for two hours without breathing ("it later transpired that he was encased in a glass box with a supply of oxygen").

No single book could ever describe the full complexity of contemporary China, and Fenby has made tough but judicious decisions about what to leave out. Perhaps the most regrettable omission, though, is the neglect of Chinese culture. Although the pace of life in China can often seem too frenetic to permit anyone to settle down long enough to write, film or paint anything, its flourishing literary, cinema and art scenes offer fragmentary but intensely individual insights into this confounding country  a welcome counterbalance to the big headline stories about industry, GDP, diplomacy and political succession. But as a one-stop guide to political and economic realities in China today, Tiger Head, Snake Tails is fast-moving, informed and illuminating.

 Julia Lovell's The Opium War: Drugs, Dreams and the Making of China is published by Picador.