If this were a selection of tea rather than a book about it, it would not be a blend: rather, it would be a box of different grades and tastes, some in well-contained sachets and some loose leaf and spilling all over one another. If I had not previously read books about India, China, the East India Company, and the opium trade (and listened to a podcast about the Boston Tea Party), it would have been hard to make sense of it all.
If you pick up the book, use the subtitle as your road map. Leaving out the personal reminiscences, which are piquant but not particularly valuable, the early chapters are about addiction. Moxham makes the case that "all the tea in China" was one of the main reasons the British wanted to get Chinese people addicted to opium: so the British would have something the Chinese actually wanted to buy from the less advanced British civilization!
He also shows how the British and, after them, the North Americans became addicted to tea, at least psychologically. The tea trade in the 18th century led to the equivalent of gangs and drug warfare, because tea was so highly profitable. For the same reason, throwing tea into Boston Harbor was a highly effective protest. By the 20th century, the UK had to ration tea during World Wars I and II because it was considered an essential good for wartime morale. That is one powerful substance.
The middle chapters show how the cultivation of tea was inseparable from the exploitation of Asian workers. At first, the British thought they had to bring tea from China to India, and to bring Chinese tea growers over, too, for their supposedly expert knowledge. It was a revolution when they realized that native tea trees in Assam, and especially Darjeeling, could flourish better than the imports. But like the growing of opium poppies and the manufacture of the smokeable version, the growing and fermenting of tea led to outright slavery, indenture, debt peonage, rape and sexual exploitation, overwork, malnutrition of workers, and trickery to get them to move to places where they knew no one and where the master was a law unto himself.
In Ceylon (now called by the indigenous name, Sri Lanka) the tea season was the obverse of the rice season on the mainland, and Tamil workers were sent from one to the other the way that Mexican "wetbacks" used to be sent from Mexico to the U.S. Southwest for the harvest (and then expelled)
Inherent in the whole story but increasingly at the forefront in the later chapters is the role that tea played in empire. I learned that British colonial rulers backed plantation owners for the profit they returned to the government even though they regarded the tea growers as low-class and uncouth. (Apparently indigo growers before them had established that reputation.) At first, the armies that protected the tea growers were those of the East India Company (another parallel with the opium trade). Later, the industry was under the control of the British empire itself.
Along with the horrors described in the book are anecdotes about how tea replaced coffee, how tea gardens and teashops at railway stations made it a common, national drink in Britain, and how Twinings made its name and survived as a specialty teamaker while Lipton overexpanded and went bust in its own country while remaining the most common Ceylon tea drunk in the rest of the world (as of twenty years ago, at least). There are also economic statistics, and battle stories, and gossip about rich colonialists and planters. I see that some readers even would have liked the author's personal experience growing tea in Africa to have been the whole book!
As for me, it contributes to my growing understanding of how British imperialism affected Asia and set different countries (and populations within countries) against each other long after the sun did set on the British Empire.