Going to have to piggy back on what ZPQ is saying (with this
link!)
tl:dr; you need to have more than just a story. What you have is a "mod story" not a "mod idea." A mod "idea" is something that has game mechanics behind it. How do you want people to play? What is the goal of the game? What emotions do you want to have and when? More importantly: What are the game mechanics? How do things work? Do you know if they will work?
On does not simply just walk into game design. As the article i linked mentions, just because you are a fan of games, and consider yourself a good judge on how good a game is, does not mean you are a good judge on making a good game. If we here decided to make our own FPS just based off an idea, it wouldn't get far. Just because we map for TF2, an FPS, does not mean that we are good designers of FPS games (though, some people like to think they are).
You will need to show that you can bring a lot more to your dev team than just an idea.