Actually, the CP/M card with a Zilog Z80 was not an
uncommon Apple II
option.
OK, it was a plausible plot line, and I'm the ignorant one. I never used either
the Apple II or CP/M to any great degree but I forgot that I actually have seen
those Apple II plug-in boards with Z80s on them .. should have recalled and put
2+2 (Z80->CPM) together.