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.



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Episode complete credited cast:
Charlene Masters
Richard Derr ...
Commodore Barstow
Arch Whiting ...
Assistant Engineer
Christian Patrick ...
Transporter Chief
Eddie Paskey ...


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


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Release Date:

30 March 1967 (USA)  »

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Technical Specs


Sound Mix:


Aspect Ratio:

1.33 : 1
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Did You Know?


Along with Star Trek: Friday's Child (1967), this is one of the only two episodes where outdoor planet scenes were filmed both on Desilu Stage 10 and on location (both times at Vasquez Rocks). Originally, all planet-side scenes were scheduled to be filmed on location, but due to the turmoil during production, director Gerd Oswald couldn't finish shooting at Vasquez. Matt Jefferies and the art department prepared a spot on Stage 10 which could accomodate the missing "alternate universe" sequence. See more »


When the fire starts in engineering, and the assistant engineer drags Masters out of the room, when they are almost to the door the smoke in the room is still relatively light, and there is not enough of it to obscure vision, but less than 3 seconds later when the door to the corridor opens, the smoke is so thick that it is not possible to see through it, a solid wall of smoke. See more »


Spock: What of Lazarus?
Capt. Kirk: And what of Lazarus?
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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 »


Referenced in Weird Science: Magnifico Dad (1994) See more »

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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 (California) – See 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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