TOS Season 1 Episode 3 Where No Man Has Gone Before

Throughout all of Star Trek there are episodes dealing with god-like entities, and a few that deal with a regular person gaining god-like powers (I’m looking at you Hide and Q). It’s an interesting way to tease out human nature by putting a character in this type of extraordinary circumstance, and I think Where No Man Has Gone Before does a good job exploring these ideas. This episode has its slow bits, but Mitchell and his relationship to Kirk are pretty compelling, lending a more organic set of stakes to what becomes a fantastical story; you both fear him and don’t want him to die.

Plot

The USS Enterprise is on an exploratory mission to leave the galaxy. En route, a damaged ship's recorder of the SS Valiant, an Earth spaceship lost 200 years earlier, is found. Its record is incomplete, but it reveals that the Valiant had been swept from its path by a "magnetic space storm," and that the crew had frantically searched for information about extrasensory perception (ESP) in the ship's library computer. The recording ends with the captain of the Valiant apparently giving a self-destruct order.
Captain Kirk decides that they need to know what happened to the Valiant, and the Enterprise crosses the edge of the galaxy. There, it encounters a strange barrier which damages the ship's systems and warp drive, forcing a retreat. At the same time, nine crew members are killed and both helmsman Gary Mitchell (Gary Lockwood) and the ship's psychiatrist Dr. Elizabeth Dehner (Sally Kellerman) are knocked unconscious by the barrier's effect. When he awakens, Mitchell's eyes glow silver, and he begins to display remarkable psychic powers.
Mitchell becomes increasingly arrogant and hostile toward the rest of the crew, declaring that he has become godlike, enforcing his desires with displays of telepathic and telekinetic power. Science Officer Spock comes to believe that the Valiant crew members might have experienced the same phenomenon, and destroyed their ship to keep the power from spreading. He advises Kirk that Mitchell may have to be killed before his powers develop further, but Kirk angrily disagrees.
Alarmed that Mitchell might take over the Enterprise, Kirk decides to maroon him at a completely automated lithium-cracking facility on the remote planet of Delta Vega. Once there, the landing party tries to confine Mitchell, but his powers have become too great. He kills navigator Lee Kelso by telekinetically garroting him and escapes by knocking out Kirk and Spock, taking with him Dr. Dehner, who has now developed ESP powers of her own.
Kirk follows and appeals to Dr. Dehner's humanity for help. Before Mitchell can kill Kirk, Dehner attacks him using her powers and weakens him. Mitchell fatally injures Dehner, but before he can recover from the effort, Kirk uses a phaser rifle to create a rock slide, killing Mitchell.
Back on the Enterprise, Kirk makes a log entry that both Dehner and Mitchell gave their lives "in performance of duty". He explains to Spock that he wants his friend's service record to end positively: "He didn't ask for what happened to him."