[Lakshya]

Which book should I buy on TOE which should not be for laymen and should contain mathematical part of the theory and advanced TOE topics.

[neutralino]

Well, the problem here is that we do not have a theory of everything, and thus there will be no books you will be able to read! There are, however, possible theories of everything; string theory, LQG, etc.. If you really want to learn about, say, string theory in a formal sense, then Zwiebach's A First Course in String Theory is somewhat standard for an introduction.