Nightbreed Anthology

I'm trying to think of a story idea for a future anthology (to be released by Tor Books) based on Clive Barker's "Nightbreed"/Cabal. Obviously, to be published in  the anthology would be a dream come true. But I've never written fanfiction (basically that's what it is). and I just don't know where to begin. The deadline is the end of September, so I guess I know what I will be doing this summer!