A Clever Quick Cryptic Nina

Well. This was a bit unexpected. Just before we started our walk yesterday, I got an email from the  crossword editor of The Times...

"Hi John, 
Since you asked about last week's "Quick Cryptic" Nina, this week's is not at all quick but very cryptic Regards
Richard
Slava Ukraini"

Firstly, for the uninitiated, a Nina is a hidden theme or motif. They are named after the daughter of US artist Al Hirschfeld, whose name he hid in most of his artwork. So (as there was last week) there is a Nina in today's Quick Cryptic. Before you read further, if you would like to try the crossword and find it for yourself, see here. (Times subscription required).Well I guess I gave something away with the picture at the top. When I got home I replied to Richard, suspecting things were not as simple as they seemed...

"Hi Richard,

 Thanks for your message. Sorry not to reply sooner – I’m just back from walking a stretch of the Angles Way some distance away. But I did solve the QC before I went and spotted the theme, although I’d never watched the program. I do enjoy your puzzles!

 Kind Regards,

John.

Heroiam slava!"

I had solved the crossword and googled to find the TV series mentioned across the top row, Gravity Falls before leaving home in the morning. Nina found. Or was it? Then it got more interesting. I got a reply in the evening after most commenters had commented on the puzzle.

"The theme goes a lot further than anyone spotted. I didn't think anyone would spot it, and I'm not sure whether to let on!"

I told him not to let on and posted on the blog for the crossword.

This is what my solution looked like annotated to show the superficial Nina...

I got this reply...

Oh. That's what we needed.. Yes there must be something encoded. And my fellow Weekend Quick Cryptic compiler Sawbill was the one who spotted it.

The clue for 25A, as well as being a perfectly good clue for ENCODED...

(the first letters, "letters beginning" of Each Numbered Clue Offer Des's Excuse Duly, definition "disguised")....

is also an instruction on solving the real Nina!

So, following  this link in the link L-Plates found, you can enter the first letter of all the clues of the crossword up to 11D...

...click on "Flip it a round" and get this..

Add some punctuation and you get a message to a character in the show who didn't get a mention in the grid..

"SORRY SOOS. NO ROOM DUDE. DES."

And that is the real Nina... and surely one of the cleverest and most elaborate I've seen! Thank-you Richard (aka Des) - yes this was one of the editor's own crosswords. And also to L-Plates and Sawbill for getting to the answer. What fun!

I got a further email...

"Well done! I didn’t necessarily expect anyone to spot it. I was watching the entire two series with my son during August 2021 and when it came to thinking of a Nina it was an obvious choice. And then, well you have to include an ENCODED MESSAGE. Wouldn’t be right otherwise :-)"

Quite right. And beautifully executed.