Hi, Nathaniel:
Abstract algebra seems to me a much clearer point of
reference than "game theory". You will find many books,
classes, and journals devoted to abstract algebra topics.
Game theory as a topic is treated from a variety of
perspectives: operations research, evolutionary biology,
political science, etc. At any rate you would probably
want to plan a graduate program in mathematics around
a base of core subjects, including abstract algebra, and
pursue "game theory" as a reading subject or applied
mathematics course.
If you are looking for readings to undertake immediately,
it might be helpful to explain a bit more what background
you now have.
regards, chip