Table of contents
Harlambos and Holborn is a reference book that is often used while preparing for the sociology optional. It's a more than 1500 page book that covers the breadth of the subject.
But for UPSC CSE purposes you don't need to do the entire book.
All that you need to cover are these topics ticked below.
Join Sociology Comprehensive Course
With KCS sir (Ex-IAS) as your faculty.
Get direct feedback that helps you improve.
Introduction - Sociological Perspectives
Chapter 1 - Social Stratification
Chapter 2 - Sex and Gender
Chapter 3 - 'Race', Ethnicity and Nationality
Chapter 4 - Poverty, Social Exclusion, and the Welfare State
Chapter 6 - Crime and Deviance
Chapter 7 - Religion
Chapter 8 - Families and Households
Chapter 9 - Power, Politics and the State
Chapter 14 - Methodology
Chapter 15 - Sociological theory
This will form the foundation for your understanding of sociology, which must then be supplemented by other resources.
Best of luck!