In the opening edition, a shape-changing alien satisfies its hunger for salt by feeding off the crew of the Enterprise. In later shows, the Enterprise picks up a youngster with awesome powers; a collision with a barrier at the edge of the galaxy causes officers to begin developing superhuman powers; and McCoy faces a race against time to find an antidote for a mysterious virus that has infected his crewmates.
The series begins with the usually rational Mr Spock behaving out of character. As events unfold, Kirk encounters Greek god Apollo on a distant planet; a strange object gliding through outer space threatens to destroy the Enterprise; and Kirk is transported aboard an alien Enterprise.
In the opening episode of the final series, Spock's brain is stolen and used to power a computer. In later shows, the Enterprise crew is captured by a beautiful Romulan commander; Kirk has his memory erased while investigating a mysterious obelisk; and orphans rescued from a nearby planet begin to have a strange effect on the crew.