Ah, yes, Frame of Mind. I was just about to bring this episode up.
I have an autographed copy of the script, if I remember right.
*****
Did anybody answer the question about what "The Lights of Zetar" was all about? If not, here's my take on it:
Scotty has a love interest. A Lt. Mira Romaine, a computer engineer on her way to install some new upgrades to Memory Alpha (the in-universe facility, not the real world web site). And when the Enterprise arrives, every living being there turns out to have been murdered by a non-corporeal entity, with the last one dying (and glowing in odd colors, and uttering unnatural vocalizations) in the presence of the landing party.
Mira is having strange premonitions. She'd seen the Memory Alpha deaths before they'd happened. And she has one of Scotty dying.
The non-corporeal entity returns, It turns out to be the surviving life force of the last few beings from the planet Zetar, where all corporeal life had been wiped out. And they're looking for a body to possess. Mira's.
Mira's brain circuitry pattern is changing. Becoming a match for the Zetarians. She is exorcised (by, of all things, being placed in a decompression chamber, with the artificial gravity neutralized, and pumped up at a rate that would likely have shattered her eardrums. Somehow, for reasons Ms. Lewis never bothered to explain, that drove out the Zetarians, and killed them.
I never found it particularly scary. Just very melodramatic and soapy.