As one of the oldest and most popular science fiction franchises of all time, Star Trek has offered a lot of content since its first release in 1966. Even though it continues to be primarily a science fiction story, it has also repeatedly dipped its toe into other genres, making it all the more varied and unpredictable for it.

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Some Star Trek episodes used the well-known notion that the horror genre and the sci-fi genre fit well together. They offered an intense, atmospheric story that no horror movie would be ashamed of. Each of the five original live-action Star Trek shows has episodes that cross into sci-fi horror and prove that even in the primarily optimistic future of this fictional universe, fear still continues to prevail sometimes.

5 The Original Series: Wolf In The Fold

Star Trek TOS Wolf in the Fold

The Original Star Trek series has primarily focused on the three main characters Kirk, Spock, and McCoy, but several of the episodes put emphasis on the supporting characters. Wolf in the Fold gives Scotty, the ship's chief engineer, the chance to shine. Sadly for Scotty, he's accused of a murder he didn't commit, and it's up to him and his friends to crack the case, and find out what happened before there's another victim.

The episode keeps the audience guessing what happens next and builds an intense atmosphere, especially when it seems like the killer is about to strike. It has an interesting link to real-life events that will surprise the viewers if they hadn't seen the episode before. An interesting fact is that the episode was written by Robert Bloch, none other than the author of Psycho, popularized even more by Alfred Hitchcock's iconic 1960 movie.

4 The Next Generation: Conspiracy

Star Trek TNG Conspiracy

The first season of Star Trek: The Next Generation was still finding its footing, and as a result, some fans consider it the weaker part of the series. However, even the first season offers several excellent episodes. Conspiracy is easily one of the scariest parts of the series, if not the scariest one. In the episode, Captain Picard investigates a mystery and faces an unexpected enemy.

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The episode has clear Alien overtones, and it builds just as impressive an atmosphere as its predecessor at times. Just like some of the best Star Trek scary episodes, it connects the detective and horror genres. It was considered so drastic at the time of its release that, for example, the BBC removed certain footage from the episode before airing it. It has components of body horror, unlike other Star Trek horror stories that use supernatural and ghost themes instead.

3 Deep Space Nine: Whispers

Star Trek DS9 Whispers

Some of the greatest fears people face in the horror genre is finding out that their friends and loved ones have been replaced by something strange... something alien. It's the basis of multiple excellent sci-fi horror movies, most notably Invasion of the Body Snatchers (1978) which happens to be starring Star Trek alumni, Leonard Nimoy. Whispers center on Miles O'Brien who comes back to the station and begins to suspect there's something wrong with all the people around him.

Whispers are one of the episodes with a surprising plot twist, and as O'Brien's paranoia and fear increase, so does the atmosphere of the story. Some fans pointed out that the episode bears similarities to Philip K. Dick's work, and the likes of Blade Runner, which is one of the best recommendations any sci-fi story could ask for.

2 Voyager: The Haunting Of Deck Twelve

Star Trek Voyager The Haunting of Deck Twelve

As an episode that even has the world haunting in the title, it's impossible to leave out this story when looking for the scariest Star Trek: Voyager episodes. Neelix tells a story about the haunted deck twelve... and to the surprise of the ship's crew, it turns out the deck is indeed haunted. Except for the fact that nothing is as it seems. After all, ghosts and spooks in space can often have a scientific origin. This one turns out to be the same in the end but not before scaring the characters, especially Neelix.

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It's interesting to confront Neelix's fear of the dark with Tuvok's primarily logical approach, which is something that causes tension between the two men. The episode offers more than one scary moment, making it an ideal watch for all fans of Star Trek. What adds to its atmosphere is also the knowledge that the crew is trapped in the Delta Quadrant, and they have nowhere to run, nowhere to hide, as their ship is their only home.

1 Enterprise: Impulse

Star Trek Enterprise Impulse

For the deeply logical Vulcan race, nothing is scarier than losing control of their base impulses, and their emotions. The third-season episode Impulse is a Star Trek homage to the topic of zombies as it features out-of-their-mind zombie-like Vulcans which makes for impressive (and scary) imagery. To make matters even more frightening, the episode starts with one of the most memorable opening scenes, featuring screaming T'Pol.

Since she's usually calm and composed, the viewers immediately understand something bad is happening, and it keeps them hooked from the start right to the finish. Another aspect that makes the atmosphere even scarier is the fact that the characters are trapped in a relatively small space, so there seems to be nowhere to run from the threat. Impulse is a space zombie horror at its best, something that's still rarely seen.

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