I was watching the STAR TREK TOS episode "The Enemy Within" on DVD and it struck me that there seemed to have been a little post-production rewriting of the story. Structurally, it makes more sense for the scene where Scotty shows Kirk that the dog-creature was duplicated to come at the end of the act, after the evil Kirk's attack on Yeoman Rand. Does anyone have a copy of the screenplay? Is this how it was written?

I don't know about the teleplay, but in Richard Matheson's original treatment the reveal of the duplicated dog serves as the Act I out...

"Kirk and Spock go to the Transporter Cabin where they are shown the sheeplike animal. Being sent through the Transporter, it has been duplicated! Stranger yet, the duplicate is as fierce and savage as the original is mild.
Kirk looks at the snarling duplicate, then at Mr. Spock in horror. "Oh my God," he murmers."

It's been a while since I've watched THE ENEMY WITHIN; how does the first act end if not with the duplicate reveal?

The last half of the 1st act goes like this:

Spock visits Kirk in his cabin and tells him that McCoy said he was acting like a mad man in sickbay.

The transporter scene where Scotty shows them the duplicated animal. (And where they obviously removed the last word from Kirk's "Oh my god.")

Evil Kirk attacks Rand in her quarters.

Spock visits Kirk and tells him about the attack. Kirk tells him that "I've been resting here since you left me."

As they leave, the evil Kirk enters Kirk's cabin.

Kirk and Spock question Rand. They mention nothing about the transporter accident. (And it is later revealed that she doesn't know about it.) Spock surmises there is "an imposter on board." Fade Out.

Next act.

Kirk, Spock, and Scotty are in the transporter room, Kirk holding the animal.


As you can see, moving the first transporter scene to the end of the act makes more sense story-wise.

Interesting.

Somebody (either Roddenberry or someone at the network) must've determined Kirk and Spock's verbal acknowledgement of the intruder to be a stronger act-out than the reveal of the "evil" duplicate. Not sure I agree but I can't think of any other explanation. Like you, I'd be curious to know if the changes were made in the draft or in post-production. Given the rigors of the TOS writing process (especially during the first season) my guess is the changes were requested prior to production -- although considering the rarity of actual TOS shooting scripts we may never know the truth; most of the TOS scripts floating around (i.e. the copies Lincoln Enterprises used to sell) are continuity drafts based on the episode's final cut.

I've got a set of production notes for THE ENEMY WITHIN at home; maybe they'll shed some light on the issue.

It looks to me like it was made post-production since the dialogue in the other scenes fits better with the original continuity.