This is a society populated by humans & "mechs". Later are biological entities very similar to humans but with subtle differences in certain genes that manifest in behaviors that are easy to recognize. Of course, humans are masters & mechs are slaves.
Now, someone (presumably human) seems to have figured out a way to enhance mechs where they're nearly impossible to distinguish from humans. And seems to be breeding them fast.
If I recollect correctly (I'd read it a few days back), the story is about a recognition by someone that such a thing is happening. And a test to recognize one specific specimen of the kind. It's not really about bursting the conspiracy.
Fact sheet.First published: Analog, January/February 2013.
Related: Stories of Kyle Kirkland.