I'll give a few examples:
- "What Are Little Girls Made Of?"
Nurse Chapel searches for her long lost fiancé, and uncovers his secret plan for galactic conquest. - "Shore Leave"
The crew of the Enterprise visits a bizarre planet, encountering the rabbit from "Alice in Wonderland", fighter planes and Samurai. - "Spock's Brain"
Captain Kirk pursues aliens who have stolen Spock's brain. - "The Way to Eden"
The Enterprise is hijacked by a criminal doctor and his loyal, hippie-like followers who are attempting to find paradise.
And here's a few from Star Trek: The Next Generation:
- "Darmok"
Picard struggles to communicate with an alien Captain who speaks in metaphors, before an invisible beast kills them both. - "Bloodlines"
DaiMon Bok returns to exact revenge on Picard, by trying to kill the son Picard never knew he had.