I think the 7 letter word becomes less random once a particularly nasty character emerges from its centre - and the theme is (broadly) 'history', after all.
But I agree - the excellent clues are the best part of this puzzle.
I’ve completed the grid , found the lines from the prologue & worked out 14 & 24 down. I can also see the words from first sentence in the grid but I’ve hit a blank on how they need changed. Maybe due to not being sure of first 3 moved words. Any hints gratefully received.
numbskull, the letters of the words from the first sentence should be changed to create a thematic word. As drxx has pointed out, the resulting word at 18 down becomes a nasty piece of work!