I apologize if this has been brought up before, but I feel the need to point out that there are NO such things as original stories - whether you like it or not you're always going to end up drawing upon some other work or tale that's been done before. What makes a piece of literature TRULY "original" is in the characterization and story-telling. The boiled down plot line does not make the story original, because it's all been done. The author's skill in weaving in the characters, the plot twists, (and in this case) the world that the characters reside in together is what builds a great story.
I've discovered that when writing, putting blinders on and striving for pure originality can more hinder you than help you. Instead of thinking up an idea, then telling yourself "no, that's been done before" and discarding it, modify your idea slightly - try not to draw off of other stories entirely, but think about what made them bad or cliche and try to work your way around that. ^^; It's difficult explaining the thought process...