Most of my work in law has been in music, with some tangents into entertainment marketing. I think I can help.
1) Keep the cover letter short & sweet. You have 15-30 seconds to make an impression-
IMHO, your letter is a bit long. Keep the portion about knowing xx, but drop
how you know the person. If xx wants to, xx can mention that tidbit if asked.
2) Move your paragraph starting "Over the past six years..." out of there. Rework the info and include it attached in a separate,
single-page resume. Include everything, including your work at Emory.
3) Ditto the plot synopsis- separate it from the body of your cover letter. When you do so, make sure you note that your work is not tied to any extant game setting or other IP- given your work history in the RPG industry, that is a question that could come up. Nobody wants to publish work connected to another company's IP.
4) If xx is willing, get a letter of recommendation or some such, preferably to xx's agent or some other person within the company you're contacting.