Reddit mentions of Introduction to High Energy Physics

What are you trying to be? Have one book just slightly deeper than Greene's book, or actually learn theoretical physics to say become a theoretical physicist or at least understand it?

If the former, it will be difficult as there's a lot of things that might be tacitly assumed that you know about more basic physics. However, a very good intro to Quantum Mechanics is Shankar. I'd also look into Foster and Nightingale's relativity book for a brief introduction to special (read Appendix A first) and general relativity. Maybe after both try A. Zee intro to QFT if you want to learn more about QFT. If you want to learn about phenomenological particle physics, say look at Perkins. Also it may help to have a book on mathematical physics, such as Boas or Arfken. (Arfken is the more advanced book, but has less examples). Also it may help to get a basic modern physics book that has very little math, though I can't think of any good ones.

If the latter than you will have to learn a lot. Here's advice from Nobel Laureate theoretical physicist Gerardus t'Hooft.