As there is an unchecked X - somewhere in the grid - I was hoping that, as an additional treat, ALL the unchecked letters would be found in the crossword's title and setter, but, alas, it seems not. As it is, I can't see that the title is very relevant, other than as an example of the theme. Or am I missing something?
[ Too late, malone (#21). I already found this hint over there at post #6 - but thanks anyway. I was trying to use a papal court - or an abbreviation for it - added to the answer, but it was quite working. ]