Usual Shark difficulty! I have a pretty good idea of the 2 unclued words, but they seem to belong in the title of two very different "works". It would be useful to know where the message in the perimeter starts. Gazing at where we have to do the highlighting doesn't help either. And a pig of a Listener too. Oh dear.
Hmm...have highlighted the 18 cells with the six thematic letters but not quite sure what it's meant to represent...as Cockie says, not the easiest and my verbal and spatial reasoning have gone to sleep now. And I can't be bothered trawling Google!