This is the story of the world's biggest drug deal.

In the nineteenth century, the British East India Company operated a triangle of trade that straddled the globe, running from India to China to Britain. From India to China, they took opium. From China to Britain, they took tea. From Britain to India, they brought empire. It was a machine that consumed cheap Indian land and labour and spat out money.

The British had two problems, though. They were importing enormous amounts of tea from China, but the Celestial Empire looked down on British goods and only wanted silver in return. Simultaneously, the expanding colony in India was proving far too expensive to maintain. The British solved both problems with opium, which became the source of income on which they built their empire.

For more than a century, the British knew that the drug was dangerous and continued to trade in it anyway. Its legacy in India, whether the poverty of Bihar or the wealth of Bombay, is still not acknowledged. Like many colonial institutions in India, the story of opium is one of immense pain for many and huge privileges for a few.