Jeff Berndt is right; ideas are a dime a dozen. It doesn't really matter how good it is; if no one is willing to write it, it isn't worth much of anything. Since most, if not all, writers are always engrossed in their own projects, there isn't much hope of selling the idea either. So the task falls to you. My advice is to start simple; maybe try it as a short story. Get the basic plot and characters down first and see where the story can go. Once you've got more of a foundation to work from, you can start expanding it into a novel.
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