Dark Knight Sequal Plot

What do you think would be the story of the next movie, if ever there would be another one? Of course there would be a new villain, but what I would want the plot to be is that this villain would remains anonymous only to batman and very mysterious, and the thing is he couldn't solve the case. And knowing the Joker's psychopathic ability, he consults him and asks for advices on how to catch the son-of-a-b*tch. But after the villain is revealed and captured the joker gets away and the last shot would be him talking to batman on a phone somewhere in some distant island and he walks away. The End. And a good title for this film would be silence of the lambs. But of course they would get sued. So I guess it would be better to give it another title. No worries, they managed to dodge Micheal Mann so i guess Nolan would be able to pull it off again...