I found this quite a struggle, for a few reasons:
- tough (but fair) clueing, which had me reaching for the BRB (and LRB) more often than usual
- an incorrect guess at the theme (two suspected thematic answers did turn out to be so, but my assumed theme was wrong)
- the brevity of the preamble, which seemed too vague and kept me asking 'but what if ... ?'
- the endgame
For too long I was daunted by a near-complete intermediate grid and I wasn't sure quite what to do or how to get started on the endgame, so I guessed at two theme words and gritted my teeth. Once underway the process proved to be quite logical. Three more theme words showed themselves, but I was halted in the final stages by uncertainty surrounding one answer whose clue's wordplay I still don't fully understand (this clue has already been mentioned, so at least I know I'm not alone). I was also missing the sixth theme word, which seems slightly questionable now that I've found it.
So even with an almost complete final grid, just one unsolved clue made finishing difficult. The puzzle might be rendered unsolvable without a near-full set of clue answers, especially when the mechanics of the endgame aren't understood.
Anyone who polished this off by Saturday has my admiration. My head hurts.