I haven't revisited it in decades (though I still have my original copy), so I can only barely recall the plot. I've since learned that it was based on a spec script the author had submitted to the Trek offices during the Original Series' third year. Supposedly, Roddenberry liked it, but as the show was canceled without a fourth season, the script was never produced. A decade later, she adapted it into a novel for Bantam Books.
I may not remember the story very well, but I never forgot the striking cover art. Here's a scan of the original cover painting by the masterful Bob Larkin, found online.
