From the publisher:
The holdings of the British Empire included present day Pakistan, Bangladesh, Sri Lanka, Burma, and parts of Iran and Afghanistan. It was an area comparable in size to the continental United States, or Europe west of the Ukraine.
The historical background and religious traditions of the Indian subcontinent rival those of other regions such as the Middle East and China. Humankind has lived and worshipped here for millennia. India is a fertile place, and there is much room for the Mythos to fester and grow.
This book is designed to provide enough information to set Call of Cthulhu adventures and campaigns during Gaslight India (approximately 1890 a.d.).