This is one of my favorite stories as far as how an idea came together for me.
So I had sent Soul Siblings (see below) to Black Gate - and got an encouraging rejection from the editor. The one comment he did have was that he simply saw too many stories about assassins. So, having heard that the best way to catch an editor's eye is to respond to criticisms within a couple weeks with something that addressed them ... I decided to write a story about characters who had unusual professions.
Now, I already had a daserii or dicemaker character who I happened to enjoy a great deal - I'm still trying to sell her original story. After some thought, I decided that someone who did clockwork would be interesting - but what in the world kind of plot would require those two sets of skills?
Fighting to work this out had me come up with the idea of villains who wanted to make a very powerful set of dice out of fatestone. And to keep the fatestone out of their hands (initially), I put it behind a massively complex clockwork gate. I ran into a number of other problems, including how you could create dice with changeable faces, but once I had the initial idea, I was off and running.
One thing I'm particularly pleased with in this story are the villains. I like to think that in some respects, their motivations (or one of their motivations) are sympathetic, and they have redeeming qualities. They're not just cackling black hats.
I've written a second story with Pazia and Vanchen, and somehow managed to get an equal amount of mileage out of their two skill-sets. Can I make it three? We'll see if another idea strikes.