This idea popped up in my head and it won't leave me alone, so I might as well share it with all of you.
What if there are dragons on Earth, who are manipulating the human race for whatever reasons they have? What if, by taking human forms, they take over governments, religions and crime syndicates?
And that's pretty much what I have right now. The dragons are ambitious, to say the least. There might be some humans with dragon blood, even if they look like ordinary humans. Some big dragon will be the BBEG, probably Tiamat. A knightly order of some kind will probably oppose them. (Knights of Bahamut?)