Recommended books that cover "Paradise Lost" by John Milton about why Satan was the protagonist?

Ok, I have to do a research paper and the topic have to be about why Satan was the Protagonist in "Paradise Lost". Now, I can not have any more than 50% of my resources from the internet, so now I am stuck finding books but I do not know where to look or even begin. A book that analyze why Satan is the protagonist or some books that break down each section and analyze what happened would be perfect or me. I don't plan on reading the 13 books because I simply don't have time for that. This is due in 2 weeks and I need to start gathering backup to support my claim.