This sounds like you have a theme or a truth.
I usually get to this point after I have some characters and plot.
However, what you can do now is go one step "up" and determine the theme topic, usually a single word describing the central topic of the story (see the linked page).
What I usually do from this point is to brainstorm a few alternative truths on the same theme, and most importantly, brainstorm a few lies that contradict this truth.
As I mentioned, I usually have characters and story so I will have someone behaving in a certain way and trying to figure out what truth or lie they would employ to do that, and also how it relates to the main theme or main truth.
Also worth noting is that while I have this construct, I always allow characters and story to go against this. The theme will never be a solid, clear aspect of a novel. If it is, the risks are the novel is too simplistic...
Another step to take is to create a one-sentence summary. Randy Ingermanson describes it in his article on the Snowflake Method.
In your case, when you only have this basic idea, I suggest either brainstorming characters and plot to outline your novel (if you like to create stories from outlines—there are several methods you can find on the net or in your bookstore.)
Or use the Snowflake Method linked above.
Or simply sit down and write whatever comes into your mind (by the seats of your pants, as it's called.)
In my case, I've done both, even though I think the initial "impulsive writing session" was actually part of outlining. I had to write to figure out story and characters and then I had to outline to get it all into a usable... second draft?
Everybody has their own process, so don't be afraid to experiment and try what works for you. Failing is just one successful way to figure out how it cannot be done...
Finally, your theme/truth is valid. I use it for some decisions in my life, so you don't have to change it, it's just, apparently controversial to some people, but that's how a good theme/truth should work. Have some people nod in agreement and others claim it's false... The more controversial, the more news coverage, the more books sold... just ask Dan Brown...