After mastering calculus, there isn't a single book that encompasses all the mathematics a theoretical physicist might need, as different physicists utilize various mathematical tools. Recommended starting points include "Mathematical Methods in the Physical Sciences" by Mary Boas and "Advanced Engineering Mathematics" by Erwin Kreyszig. Essential mathematical topics for theoretical physicists include vector and linear algebra, tensor algebra, vector and tensor calculus, analysis, functional analysis, probability theory, Hilbert space theory, and elements of Lie-group theory. It's crucial to focus on understanding how applied mathematicians present their results and how to apply these concepts to specific research areas in physics, as the mathematical requirements can vary significantly between theoretical and experimental physics.