"Where No Man Has Gone Before" was the second pilot episode of the original series of Star Trek. Unlike the first pilot, "The Cage", Captain James T. Kirk is in charge, with a promoted Mr. Spock as his first officer; but Leonard McCoy is still missing.

The Starship Enterprise is sent on a mission to try and exit the galaxy; all previous attempts at this had failed. En route, it discovers a black box left behind by the last ship to make the attempt, the S.S. Valiant, which reveals only that just prior to the destruction of the ship, the crew had been searching for information about extra-sensory perception.

When the Enterprise reaches the edge of the galaxy, Kirk's friend, Lieutenant Gary Mitchell, is changed somewhat. He gradually becomes more mentally powerful and eventually develops psychokinesis. A ship's doctor, Elizabeth Dehner, also exhibits similar symptoms, and the two become close.

Mitchell becomes increasingly arrogant, declaring his wish to rule over humans. Kirk is forced to exile them to a remote planet, but they escape. Eventually, Kirk corners them. Dehner turns against Mitchell, and is killed by him; whilst Mitchell is distracted, Kirk manages to kill Mitchell himself.

Curiously, Kirk's middle initial is given as "R." in this episode. "T." was evidently selected later, with this episode being overlooked.