I have finished the puzzle, including finding the author, the 6 names, and the alternative names for the 6th character but I'm still puzzled about the clash I have where 12D crosses 20A. I realise that the two letters that could fill this cell actually represent character 6 but this doesn't seem to be mentioned in the preamble. Have I made a mistake with one, or both of these answers? I can move on once I know!
12dn is a straightforward anagram of o+sent followed by ep, so I'm sure you have that. Which leaves 20ac. DRO(P) is almost trap, and then you have D in ST(A)Y, with A the extra letter. So I had Drostdy, and no clash
Thanks Turnerjmw. I'm totally stupid! I had both of those answers pencilled in faintly - then, days later, I misread my own writing and inked in an "i" making DROSIDY. I should have checked again with Chambers. Doh!!