TOS - Lights of Zetar

Plot: Scotty's romance with a new Star Trek officer is interrupted when aliens attempt to take over her body. 

Pros:  Guest star looks good in a short skirt.  Memory Alpha,  Conference to solve the problem
Cons: Bad romance, dull guest star,  Scotty plays the fool,  another bottle episode, plodding story

Quite rightly considered one of TOS' worst episode, there's really nothing terrible about LOZ, its not And the Children shall Lead,  it just covers familar ground and is very mediocre. Designed to appeal to a female audience, we get some standard 3rd Season tropes;

• A plot centered on a female guest-star (Mira)
• A romance (this time with Scotty)
• Aliens taking over a human body
• A bottle episode 

The script is pedistrian and the execution is poor.   Scotty is written as a love-sick mooncalf,  Gushing over Mira, and being overly-protective. Its hard to believe this version of Scotty has ever seen a woman before. Mira, meanwhile,  never even smiles at him. Her love for Scotty only appears at the end.  And the two actors (Doohan and Jan Shutan) have zero chemistry. Its a very odd romance.  

And while Shutan isn't bad in the role,  Mira - as written - isn't particularly likable or interesting.  She snarks at McCoy, and is often strong-headed and egotistical for no reason.  And that's a big problem, because there's nothing in the story  itself that's interesting.  Shatner, Bones, and Spock, help solve the problem and "cure" Mira, but she's really the center of the story.  A space battle with the alien lights, and a few dead people on Memory Alpha are thrown in, to gin up the action,  

Typical Bad Scotty Dialogue

SCOTT: You're the sanest, the smartest, the nicest woman that has ever come aboard this ship.
MIRA: Anything else?
SCOTT: Anything else, I'll keep to myself for the moment.

And:

KIRK: Get to Sickbay, Lieutenant. That's an order.
MIRA: Yes, sir.
SCOTT: Captain, would it be all right if I went along to Sickbay?
KIRK: No, Mister Scott. Stay at your post for the moment.
SCOTT: But Captain

Summary:  "The Lights of Zetar" is so bland and boring its hard to write about.  A talky, talk fest on the Enterprise, it plods along from A to B.  The aliens aren't particulary interesting either,  they just want to live.  Nor is the resolution exciting or belivable.  Given all that, the central character Mira, needed to be something special - and she's not.  Skippable.