Hello, I'm another lurker finally moved to post for the first time. First I want to say thank you to all the regulars on this forum whose wisdom I've benefitted from each week as a crossword newbie.
Recently I thought I'd been doing quite well, but came completely unstuck this week. Like some others, I'm doing the paper version so was missing the vital special instruction until I read this forum. Then I stared at chrise's hint for ages, but still couldn't figure out what was going on. In case it's helpful to anyone else still struggling with the theme, it was 13a that helped the penny drop for me. It seemed to be missing a definition. I figured out a likely letter for it to begin with, and then had an idea of the answer from that and the two crossers I had. Then I remembered something that paradigmshifter had said and bingo! My son has a useful aid in his room that helped us fill in the other themed clues. I'm not done yet, but feeling much less bamboozled - thanks all.