Star Trek (1966–1969)
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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)

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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 »


Official Sites:

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Release Date:

30 March 1967 (USA) See more »

Company Credits

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Technical Specs


Sound Mix:




Aspect Ratio:

1.33 : 1
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Did You Know?


Lazarus' costume was later worn by an extra playing a Babel Conference delegate in Star Trek: Journey to Babel (1967). See more »


The Enterprise crew, and Starfleet, refer to a portion of the galaxy as 'quadrant', and later, as 'Section'. It is likely they meant 'sector', which is a lot smaller than a quadrant (one fourth of the galaxy). See more »


Assistant Engineer: Hi.
Charlene Masters: Hi. Coffee?
Assistant Engineer: Is that an order, Lieutenant?
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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 Galaxy Quest (1999) See more »


Theme From Star Trek
Written by Alexander Courage
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User Reviews

Only the explanation in the last 5 minutes is interesting, but by then it's too late
21 January 2016 | by pkottaSee all my reviews

Yes, it's true, this is one of the worst episodes in the entire series, right down there with "The Empath." Yes, Lazarus is one of the most irritating characters, always falling off cliffs to move the story (such as it is) along.

The *only* thing that's interesting in this episode is when Lazarus finally explains how his cat-and-mouse with his alternate-universe counterpart came about. Both the sci-fi physics element and the madman element of the premise are fascinating. But this explanation comes in the last 5 minutes of the show, after 40 minutes of exhausting shenanigans -- too late to even buy the "r" in the word "redeem."

I would love to know the backstory about how this episode went from fascinating concept to crummy filmed episode. Perhaps that would help ease the pain that this entry's very existence creates in the beating heart of the series.

Another interesting bit about this episode is that with it, the series nearly bottoms out before rocketing to the top with the very next episode, "City on the Edge of Forever." From the very bottom, the only way to go is up.

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