The very first meta I posted on this here site was called "Mystery Theme," so it seemed appropriate to call this one "Mystery Theme 2." All I'll tell you is that the meta answer is the solution to the mystery. I highly recommend solving the pdf (pdf solution), because the exact shape of the grid doesn't show up in the puz. (I'm including the puz just for convenience's sake, but if you solve it, please do take a look at the pdf too.)
As always, shoot me an email with answers/requests for hints/etc.