"The Enemy Within" marks first contact for Star Trek with the evil twin trope, as Kirk gets split into Picard and Archer in a remarkable episode eventually surpassed by a famous goatee later in the series. Richard Matheson's plot contrivances and physical absurdities (creating matter out of what?) may make poor science fiction but serve adequately as a lesson into humanity, as Spock says, "an unusual opportunity to appraise the human mind, to examine the roles of good and evil in a man." The story more or less writes itself, down to a unifying conclusion with only a fuzzy horned poodle thrown in for suspense (and couldn't they simply stun evilPoodle instead of hypoing it?), so it's up to the acting and here William Shatner excels. His evilKirk, leering through the decks guzzling Saurian brandy, often and unfairly overshadows his thoughtful portrayal of goodKirk: kind, compassionate, and above all wishywashy.

"Second Officer" Spock insists upon the only logical answer (an imposter) though he doesn't explain (because he's insensitive?) why an imposter makes Kirk appear unaffordably vulnerable or otherwise less than perfect. "Stun all Kirks until we have two of them" is quite the logical plan even if goodKirk doesn't right go ahead and announce the imposter anyway! So much for logic. McCoy makes cogent points about man's essential courage arising from his intellect plus he gets his first chance at his by now famous pronouncement, "He's dead Jim." A suffering Sulu (since Chekov's not onboard yet!) gets good time as does Scott who hopefully recognizes how this soft magnetic yellow ore could be turned into a powerful anti-transporter weapon. Grace Lee Whitney also gets an extended chance to perform (though she fights back, an interesting appearance wouldn't you say Yeoman?).

For this episode one should dial the suspended disbelief knob down to enjoy the good elements without regard for the holes between them, because there are a lot of wholes such as ignoring the obvious solution of sending a shuttle to the surface to rescue the landing party or beaming down inanimate combustibles (not gonna touch, "The lower levels - the engineering deck"). But then again can't Sulu and his three mates build any better shelter than a wall of rocks and a flimsy blanket? Maybe if he wasn't snarking so much about coffee or ricewine! It also takes needless dips into technobabble that answer questions artificially staged by an already shaky premise, ignoring of all questions the curiosity really exposed: Why does the captain have face makeup in his cabin?