Concept/ideas can 't be protected via copyrights, their specific expressions may be.
So, flesh up your story in sufficient detail , get a copyright on it and then present it to prospective buyers. This is always a grey area since the prospect could, after seeing your story, claim that he had anyways thought of it already. But you will have to take your chances- where it is better to deal with reputed media houses, maybe via agents.
For some interesting thoughts on this see :