“The Last Mughal” (Knopf, 448 pages, $30) counts as a snappy title for the man whose subjects addressed him as “His Divine Highness,” “Caliph of the Age,” “The Shadow of God,” “Offspring of the House of Timur,” “Mightiest King of Kings,” and seven other names besides. With so many names to choose from, this “Emperor, son of Emperor” simply went by Zafar when he turned to composing his melancholy lyrics in the moonlit formal gardens of the world’s greatest palace complex, the Red Fort. As the sole heir to the remnants of the Mughals’ 350-year-old empire, Zafar had titles to burn. But by the time this story finds him, aged 77 in the middle of the 19th century, he is frail, henpecked, indecisive, and all but overthrown. Another, newer empire had cast its long shadow across the Shadow of God. Within a few turbulent years, the British East India Company reduced him to “the Delhi State Prisoner.” A decade later he lay buried in an unmarked grave.

Zafar, who sounds like the most charming kind of despot, is not exactly the subject of William Dalrymple’s new book. The subtitle hits much closer to the mark. This book is the lengthy yet concise story of Delhi at its most critical juncture. In his dotage, Zafar represented his family’s decline as it teetered into the second half of Britain’s great century in India. He and his court were culturally refined, yet politically and financially vestigial. Zafar’s reign was supposed to be the whimper of his world’s end, but instead it went off with a hell of a bang: what the British refer to as the Indian Mutiny and what Indians call the Uprising.

The cataclysm of 1857 was “the most serious armed challenge any Western empire would face, anywhere in the world, in the nineteenth century,” Mr. Dalrymple writes. Of 139,000 sepoys employed by the Bengal Army, all but 8,000 turned against the British. The outcome of this rebellion was impossible to guess through several months of fierce fighting across northern India and still difficult to fathom even after the British had prevailed. Tens of thousands were slaughtered and many more died of cholera or starvation. The war terminated the Mughal dynasty and transformed the East India Company into a branch of the British government. Delhi was reduced to a “city of the dead” and with its ruin, Mr. Dalrymple argues, “the beating heart of Indo-Islamic civilization had been ripped out, and could not be replaced.”

Mr. Dalrymple excels at the devil of the details. In his hands, the minutest stages of the catastrophe find gratifying color and orientation. For Delhi’s purposes, the uprising was sparked by the mutiny of thousands of sepoys stationed in Meerut, 40 miles away, on May 11, 1857. Most of Britain’s fighting force was comprised of high-caste Hindu sepoys drawn from the cities and countryside far to the east of Delhi. Disaffected regiments of Hindus and Muslims rebelled almost simultaneously across the region, quickly killing their European officers and then turning, in hopeful desperation toward Delhi. (Mr. Dalrymple lends some credence to the old chestnut of their having rebelled at the offense of having been made to bite into rifle cartridges greased with pig and beef fat.) The forces congregated at the old Mughal capital, drawn by the prestige of the emperor and the wild dream that under his banner Indians of both major religions could rise up and expel the British and their Christian converts. Mr. Dalrymple vividly reconstructs their movements that day, isolating the times and text of the British telegraphs sent in distress, the garments Zafar wore, and the slogans shouted by the excited mutineers.

The day erupted into a massacre of the British who were stationed in Delhi. The sepoys, who must have been nearly as terrified as their victims, demanded of the startled and peaceable king that he give his blessing to their cause. The king dithered, and then finally acceded, thus beginning a five-month nightmare, pitting the sepoys (and soon many civilian Muslim “mujahideen”) against the surviving British and their camp followers. Mr. Dalrymple explains the confrontation as a religious war, albeit a very strange one:

Where a Muslim Emperor was pushed into rebellion against his Christian oppressors by a mutinous army of overwhelmingly Hindu sepoys, who came to him of their own free will (and initially against his) to ask for the barakat of a Muslim blessing and the leadership of the Mughal they regarded as their legitimate ruler.

The result was bloody murder all around, worst of all when the victorious British finally succeeded in storming Delhi for their revenge and their “loot” (the Hindi word was just passing into the English language).

Mr. Dalrymple has been writing persistently about Delhi since publishing “City of Djinns” in 1993, but in recent years his style and ambition have turned from those of the English travel writer, enchanted by a sense of a history, to serious scholarship, still blessed by his gift for finding eye-catching transitions, strong characters, and a knack for turning indigestible tracts of historical documentation into a roaring good story. In Zafar, Mr. Dalrymple has found a wonderfully humane symbol for the melancholy decay, confusion, and collapse of a city he loves. Delhi had been crushed before and of course it has grown back to become one of India’s largest cities, with a population well above 10 million. But the Delhi of the Mughals, what is today called “Old Delhi,” which left the capital with its best-known landmarks, died a horrible death with the sepoys’ rebellion.

The British experience of the Uprising has been told by previous historians, who have enjoyed the aid of Victorian-era letters, memoirs, and court proceedings. Mr. Dalrymple has looted these accounts for all they are worth, but the animating discoveries behind this work have been on the Indian side. Through the work of a Delhibased scholar and translator, Mahmoud Farooqi, he brings to light invaluable material from the untranslated memoirs of a minor courtier, Zahir Dehlavi, along with fragments from the 20,000 pages of “the Mutiny Papers” he claims to have rediscovered laying about unused in India’s national archive. It seems almost unfair for a book with such a fine sense of plot, physicality, and even humor to contain primary research as well.

Anyone reading “The Last Mughal” today, especially readers with no prior interest in the Mughals or the Mutiny, will find much to ponder in relation to America’s ongoing adventures in the same neighborhood. Mr. Dalrymple says as much in a historical aside about the Mutiny’s role in the creation of the Taliban 130 years later, but analogies to Iraq are even likelier to come to mind. A fishy dossier justified the East India Company’s annexation of Awadh, next to Meerut, in the first place, while “the trauma of May 11” justified what came later. Christian evangelizing went hand in hand with the hardening of native religious sentiments, in which the most Moqtada al-Sadr-like figures rose to the top of the squabbling heap. It is sad to note while reading this excellent history, which came much too late to spare Mr. Dalrymple’s beloved Delhi from British retribution, that despite his new research into the Mughal side of the fighting, we still do not understand fully the composition of the insurgency. Its grievances and its tactics remain opaque, and its mystery urgent.

Mr. Travelli is the senior editor of the Economist Web site.