The medicine required for Spock who has contracted a fatal disease is stolen by Orionian pirates.
The Enterprise crew is being observed as their suitability to meet with advanced civilizations.
The computer of the Enterprise gains partial sentience and starts playing practical jokes on the crew.
Dr. McCoy is arrested and charged with causing an alien plague.
The Enterprise runs into a being that once visited Earth and influenced the Mayan culture.
The Enterprise tries to save an unidentified ship plunging into a supernova but is dragged into a universe where time runs backwards.