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The Alternative Factor 

Existence itself comes under threat from a man's power-struggle with his alternate self, with the Enterprise's strained dilithium crystals presenting his key to a final solution.


Gerd Oswald


Don Ingalls, Gene Roddenberry (created by)




Episode complete credited cast:
William Shatner ... Capt. Kirk
Leonard Nimoy ... Mr. Spock
Robert Brown ... Lazarus
DeForest Kelley ... Dr. McCoy
Janet MacLachlan ... Lt. Charlene Masters
Nichelle Nichols ... Uhura
Richard Derr ... Barstow
Arch Whiting ... Assistant Engineer
Christian Patrick Christian Patrick ... Transporter Chief
Eddie Paskey ... Lesley


While investigating and scanning an uncharted planet, the Enterprise and its quadrant of space are subjected to a violent force that seems to cause a 'blinking out' of everything near them. When the scanners resume, where once there was no life on the planet, now there is one life sign. Kirk, Spock and a security force beam down to investigate and find a man named Lazarus who collapses and is brought aboard the Enterprise for treatment. To complicate things further, the initial phenomenon almost totally drained their dilithium crystals. Starfleet and Kirk suspect this phenomenon could be a prelude to invasion. While interrogating Lazarus he tells Kirk that he's locked in a struggle with another being who is 'anti life' and is behind the phenomenon. The disruptions continue to occur and the ship's situation grows worse. Written by tomtrekp

Plot Summary | Plot Synopsis


TV-PG | See all certifications »

Did You Know?


When Lazarus sabotages the Engineering Panel to create an overload, and eventually steal several dilithium crystals, the electrical plugs he switches around are actually Dual Binding Post Plugs (banana plugs), very common when this show was made in the 1960s and still in use in 2021. See more »


When the code factor one transmission comes through from Starfleet Command, before Commodore Barstow appears on screen or is otherwise identified, the bridge screen is still showing the planet below, and while the planet below is still showing, Kirk says "Kirk here, Enterprise standing by Commodore," although Kirk would have had no idea whether he was about to be speaking with a Commodore or an Admiral. See more »


Capt. Kirk: You'll be trapped inside that corridor with him forever. At each other's throats throughout time.
Lazarus: Is it such a large price to pay for the safety of two universes?
See more »

Crazy Credits

The closing credits are set against a combination background of stills from that episode and previous episodes. See more »

Alternate Versions

Special Enhanced version Digitally Remastered with new exterior shots and remade opening theme song See more »


Referenced in Suits: Meet the New Boss (2012) See more »


Theme From Star Trek
Written by Alexander Courage
See more »

User Reviews

A bit of a klunker.
15 June 2009 | by BlueghostSee all my reviews

According to "Star Trek; the Inside Story" by Solow and Justman (the two original producers of the Star Trek series) there were some contractual issues with the actor who was supposed to play the guest lead, and thus this caused some scheduling issues which cascaded into other areas of production.

Result; this episode.

Well, what can a guy say about an installment that was supposed to be the crown jewel of Trek, but wound up being a bucket of swill? An "A" for effort... err... maybe.

Things that I spotted; there's an exterior shot showing Kirk and Spock leading a search team, but the actors are their stunt doubles, and not Shatner and Nimoy. The lead character seems prone to injury, and the science fiction in this episode is more fiction than science.

I'll say this, the reason I tend to prefer classic 1960's Trek to the TNG+ era, is because the first season of TOS Trek is psychological; the second season is sociological, while the third season is more interpersonal (with all its flaws). This episode really strove to be a true science-fiction story, and not some encoded amalgam conveying a comment on contemporary society.

No, this episode really wanted to post the question of sacrifice to save two realms of existence. As stated earlier, director Gerd Oswald wanted the son of a famous actor who had star power (the name escapes me). Said actor was drunk and didn't show up for the shoot. SAG threw the book at the actor for breaking his contract, and torpedoing what could've been an interesting, and a true first pure sci-fi masterpiece for this very memorable series.

But, blaming the guest star for all the foibles isn't fair. Truth is the writing was a little weak in this episode. Without a psychological formula to rely on this episode was truly trying to break new ground. But, because the author(s) did not know enough about the science they were dealing with, and only the philosophical dilemma of what they wanted to pose for the audience, the story falls flat.

Even so, it's still fun to see our favorites run around on the screen to save the Federation (and everyone else in this case) from a fate worse than death.

Not a sterling installment. Watch only in passing... if at all.

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Greek | English

Release Date:

30 March 1967 (USA) See more »

Company Credits

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Technical Specs


Sound Mix:

Mono | Dolby Digital (re-mastered version)| DTS (re-mastered version)


Color | Color (Technicolor)

Aspect Ratio:

1.33 : 1
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