Empire and Information: Intelligence Gathering and Social Communication in India, 1780–1870 (Cambridge Studies in Indian History and Society, Series Number 1)

This dense, rich work charts the sea changes in British intelligence in India from early colonies in contact with the Mughals to the East India Company to the Raj. It is very thorough: Bayly both digs in to the meaningful granular level of historical documents and also points out the overarching trends over decades. An excellent source for scholars or newcomers to the subject. If you are studying British India, this book will serve you well.