This from Neil Gaiman, because it can never really be said enough:
I rarely go “I will now write a …” (whatever. Fantasy, or pirate story or detective story or ghost story) and then try and find a plot. Mostly, I go “This would be a story…” and then follow it where it goes. I think that’s more fun. Worry more about your characters—are they people you would like to meet and spend time with?—and what you’re trying to say, what the story’s about, than you do what the story is. Because if you know what it’s about, then you can simply inspect and use or reject ideas.
Now, back to the Batcave.