The Enterprise is in pursuit of a small vessel. The vessel is destroyed but Scotty manages to beam off the "crew," which consists of "entrepreneur" Harry Mudd and three captivatingly beautiful women. It turns out the three women are not so much crew as cargo; they were going to be wives for settlers. But the Enterprise sustained damage during their pursuit of Mudd's ship, forcing Kirk to head for a mining colony for more lithium crystals.
- Early Installment Weirdness: Another episode with references to "lithium," which would later be called "dilithium," and Spock being referred to as "Vulcanian." Uhura is seen in the gold command uniform.
- Emergency Refuelling: Rescuing Harry Mudd's ship destroys three of the Enterprise's four dilithium crystals and damages the fourth, so they have to travel to a lithium mining operation on Rigel 12 to get more.
- Feminine Women Can Cook: Even in the future women are expected to be good cooks!
- Hidden Depths:
- Childress apparently just wanted a woman to hang around and be pretty, but starts to look at Eve in a new light as she reveals herself to be more clever than he expected.
- Mudd at first appears to be some kind of pimp or even slave trader when he insists on calling the women "cargo", but he's basically the only one who consistently treats them with any kind of respect.
- Human Outside, Alien Inside: It's mentioned in passing that Spock's heart is over to one side and further down than a human's heart would be.
- Lie Detector: During the hearing, the computer constantly replies "Incorrect!" when Mudd is lying. Mudd mutters about the "blasted tin pot" when it pulls up his criminal record.
- Magic Feather: During the reveal that Mudd was using the Venus Drug to enhance the women's beauty, Eve takes the pill. At first the drug seems to work. Then Kirk reveals that the pill she ate was just colored jello, the real drug confiscated. It turns out Eve didn't need the drug, just her self-confidence — to instantly restore her eye makeup and lip gloss and fix her hair.
- My Sensors Indicate You Want to Tap That: During the hearing into Mudd's reckless piloting, Kirk initiates a computer scan of all present intended to discover if Mudd or his passengers are showing physiological reactions indicative of dishonesty. The computer reports negative, then volunteers that most of the male crew present are showing physiological reactions indicative of attraction to the women. However, McCoy's sickbay instruments go haywire whenever one of the women walk past.
- Running Away to Cry: Eve tearfully screams that they should have a lottery with her as the loser's prize and darts outside. Kirk tries to follow her, but gets hampered by the sandstorm in progress.
- Space Western: The episode uses several well-worn tropes of the genre. Mudd is essentially a hustler selling women to settlers out on the frontier, although the implications of this are not explored in any detail.
- Sherlock Scan: Mudd apparently can do this, correctly noting that Spock is part Vulcan despite him looking like pretty much every other full-blooded Vulcan. However, this could also be yet another case of Early Installment Weirdness - both of the previous episodes to be filmed ("Where No Man Has Gone Before" and "The Corbomite Maneuver") are explicit in establishing Spock as half-Vulcan; the writers may have originally intended for full-blooded Vulcans to look considerably less human than Spock does.
- Space Does Not Work That Way: Based on the Solar System's own Belt, asteroids of that size are not going to come at a speeding ship with that frequency.