Capt. Kirk obsessively hunts for a mysterious cloud creature he encountered in his youth.



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Episode complete credited cast:
Stephen Brooks ...
Jerry Ayres ...


Captain Kirk is haunted by a creature from his past when conducting a mining survey on a planet. He first encountered it as a lieutenant aboard the U.S.S. Farragut and blames himself for freezing in a moment of crisis, causing the death of many crewmen. The creature is a cloud-like, gaseous being that lives on the red blood cells found in humans. Obsessed by his desire for revenge and to erase the memory of 11 years ago, he pursues the creature relentlessly, putting in jeopardy an assignment to collect essential medical supplies. Written by garykmcd

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Release Date:

15 December 1967 (USA)  »

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Aspect Ratio:

1.33 : 1
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Did You Know?


In an effect unique to the series, the phaser beam that Garrovick fires at the creature is outlined with a dark border. See more »


In the final trap to destroy the creature, Kirk uses a bomb baited with spare blood. They are shown to be setting up the bomb and the jar of hemoglobin is meters away. The proper way to set the trap would have been to beam the bait down once the trap is set. See more »


Mr. Spock: I hope I'm not disturbing you, doctor.
Dr. McCoy: Interrupting another autopsy report is no disturbance, Mr. Spock, it's a relief.
Mr. Spock: I need your advice.
Dr. McCoy: Then, I need a drink.
Mr. Spock: I do not understand your reasoning.
Dr. McCoy: You need advice from me? You must be kidding.
Mr. Spock: I do not joke, doctor. Perhaps I should rephrase my statement. I require an opinion. There are many aspects of human irrationality I do not yet comprehend. Obsession, for one: the persistent, single-minded fixation on one idea.
Dr. McCoy: Jim and his creature?
Mr. Spock: ...
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Referenced in Star Trek Continues: The White Iris (2015) See more »

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User Reviews

Military Drama Posing as a Space Monster Adventure
11 October 2007 | by (Vulcan) – See all my reviews

Obsession features a great Art Wallace script and solid performances by Shatner, Kelley and Nimoy. An away team is investigating a seemingly uninhabited planet, while carrying a cargo of medical supplies to a rendezvous for which they can't be late. A mysterious gas cloud attacks and kills a trio of red shirts by consuming their red corpuscles. Kirk recognizes the smell (literally) of all of this and explains that the last time he encountered this creature, half of his ship's crew was killed. The son if the captain Kirk served with is now a member of the Enterprise crew (Stephen Brooks) and Kirk believes that his hesitation doomed his crew mates. Soon, Kirk's obsessive behavior regarding the gas cloud has the crew questioning his sanity.

Ralph Senensky's direction keeps this classic Shatner episode tight, exciting, and well shot. There are many memorable scenes and the script allows for some very good character development for the young ensign as well as the principal cast members. And unlike the standard Star Trek Space Monster story, this ends up being as much a human-military (naval) drama as it is an adventure tale.

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