I think you should be pretty familiar with the end of The Motion Picture; I'd recommend seeing it beforehand. And you should probably read the Memory Alpha summary of "For The World Is Hollow And I Have Touched The Sky" too.
I actually couldn't remember which TOS episode starred the Fabrini, so I went to Memory Beta first, then to Memory Alpha.
Based on the summary on MB, I've grown more interested in reading Ex Machina. To be honest, I was a bit turned off by the back cover summary.
You should probably read the Memory Alpha summary of "For The World Is Hollow And I Have Touched The Sky" though.
Ah, that's true, familiarity with "For the World is Hollow . . ." would help. I did things all kinds of backwards. I read Ex Machina, then re-watched TMP for the first time in years, then eventually got to "For the World is Hollow . . ." during my viewing of the entire original series (thank you, Netflix!). My Trek re-watch is happening in a linear fashion, but I've kind of been jumping all over while catching up on the books. But Memory Alpha helped me understand the Yonada aspects of it. (I remember being a little confused when I first read The Lost Years way back in the day, before I could do an Internet search to understand the Yonada/Natira references.)
I freaking love Memory Alpha.
However, the death toll was nowhere near ten percent. Memory Beta gives a UFP population of 9.85 trillion sentients, ten percent of which would be 985 billion. The death toll in the Borg invasion was 63 billion total, including the Klingons, Romulans, and unaligned worlds, so the UFP toll was probably more like 45-50 billion, or around 0.5 percent. So that would not qualify as "literally decimated."
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