The argument is that poverty and low wages for Indian weavers resulted from colonial rule and emerged in the 19th and 20th centuries. During the 18th century, weavers enjoyed economic and political power and a stable position.
This is a dense, well-argued and well supported book that greatly informed my (limited) understanding of British colonialism in India. Parthasarathi documents the conditions and relationships of weavers in South India extremely well, and very clearly shows the transition that occurs in the end of the 18th century with the rise of colonial rule. To summarize, the British imported English discipline but not English rights leading to the emergence of a despotic colonial power. Parthasarathi also shows how the rise of British power was facilitated by local political and economic conditions along with indigenous cooperation.
Although this is a dense (I am saying it twice because it is really dense. That's three times) book, it is well worth the effort. It is extremely well written, it is about a subject that I am not intimately familiar with but was immensely more knowledgable about after reading, and its argument is convincing and satisfying. It is an academic text, but I would recommend it to anyone willing to put the time in.