TOS - 1.05

 "The Enemy Within" is the fifth episode broadcast of Star Trek The Original Series, airing first on October 6, 1966.

This is another winner in my mind - it holds up very well and introduces us to a trope that would be played over and over in the Star Trek universe.  My favorite variation of this is the "Mirror Universe" episodes that Deep Space Nine would perfect several decades later.

Kirk gets beamed back up, but due to transporter mumbo-jumbo he is split in two.  The "good" Kirk comes back first and is disoriented so they take him to sickbay.  Naturally the transporter room is left empty, lol wut, and "evil" Kirk shows up.

Billy Shatner absolutely tears it up with his performance as the Kirk Id gone wild!  Love his scenery chewing and over the top emoting, good stuff!

Less effective is the sub-plot to explain to the audience what is going on with a ridiculous doggie in a costume.

Though it is a useful device to give us the "ticking clock" that we need to have enhanced jeopardy and peril.  The dog dies - and so will Kirk if we don't figure this out!

The sub-sub-plot, with Sulu and his homies "chilling out" on the frozen at night planet, is also effective in pushing the stakes higher.  Too bad they don't have a shuttle craft or something...

The climax of the story is pretty awesome, with both the good and bad Kirk facing off on the bridge - it's genuinely exciting and also very satisfying when Spock and the gang easily recognize who the bad guy really is.

Also great is that good Kirk ends up actually persuading bad Kirk that they both need each other.  Another great Star Trek moment!

Also also, the less said about Yeoman Rand and her post-assault attempt to chummy up to restored Kirk at the end, the better.

So yeah, this one is probably not a top ten, but it for sure falls on the winning side.  A great plot device, that once again Twilight Zone did first - but Star Trek really masters it, and yes, uses the story again and again over the years.

Up next - one of my LEAST favorite TOS episodes ever - "Mudd's Women". Boy I really can't stand that episode!  But I'm in the middle of watching it for a second time, just so I'm really sure to give it a fair shake.  Stay tuned!