Enterprise encounters a recorder marker from the S.S. Valiant, lost two centuries before. The marker logs the Valiant's encounter with the energy barrier at the edge of the galaxy and their subsequent self-destruction after frantic attempts to research ESP. Despite the warning Kirk decides to investigate the barrier, wrecking the ship and killing several of his crew. The ship must limp for repairs to Delta Vega, a fully automated cracking station fortunately equipped with a brig. That's not the worst though since barrier passage destroys humans with mediocre ESP while producing seemingly godlike abilities in those with the strongest. (Odd that Vulcans with such built-in abilities aren't bothered at all.)

Among the effected are helmsman Lt. Commander Gary Mitchell, Kirk's friend for many years, and Dr. Elizabeth Dehner, a (disposable) ship's psychiatrist. After the barrier shocking their eyes glow eerie silver, their voices gain an unnatural echo, and they gain the powers (among others) to make apple trees and shoot lightning from fingers. Kirk tries to maroon Mitchell on Delta Vega, but Gary isn't keen on the idea and escapes with Elizabeth. Kirk chases them to a confrontation, and is almost killed until Dehner turns on Mitchell and together (plus a BIG rock) they bury him literally in the course of duty.

SF royalty and actor extraordinaire Gary Lockwood stars as the completely unlikable Mitchell, insolent, resentful, capable and willing to abuse his history with the Captain. Lockwood's wonderful acting maintains the menace of Mitchell without ever dissolving into ridicule. Paul Carr as talented thief Lee Kelso on the other hand seems a dedicated, competent officer, the type to threaten Mitchell who kills him without compassion. Sally Kellerman excels as the "walking freezer unit" who saves all with her timely prognosis. Sadly Paul Fix can't muster much as Chief Medical Officer Mark Piper, shaded by both predecessor and successor.

"Where No Man Has Gone Before" deserves credit as the episode that sold Star Trek. If anything, the least part of the effort is the visual jarring caused by style incongruities with the rest of the series, like the bridge helm as transporter, Spock in a gold shirt and wired headphone, Cage-style communicators and mini-screens, a gold-shirted Scott without a McCoy, and a Sulu in blue (but with a new helmsman job!). Told by the suits that the first pilot was "too cerebral," Roddenberry returned with this thrilling action story full of guest stars, phaser rifles, and enough pseudoscience to keep it entertaining while still grounded in the Trek-verse to come.