There is no single source for studying the whole vast subject as Political Science and International Relations. An aspirant should approach the following books for the depth of understanding - First, for Political Thought, Ideologies, Indian and Western Political Thought - O.P. Gauba for Political Thought and Theories, Brian Nelson for Western Political Thought, V.R. Mehta, IGNOU for Indian Political Thought. Second, for Indian National Movement, Indian Govt and Politics - Laxmi Kant, Bipin Chandra, and Spectrum are the recommended options. Third, for Comparative Politics - IGNOU MA Modules (selectively, topic-wise from syllabus), Global Politics - Andrew Heywood for in-depth conceptual understanding. Lastly, for International Relations - Challenges and Strategies - Rajiv Sikri Does the Elephant Dance - David Malone