Star Trek: The Next Generation picked up the noble mantle laid down by Captain Kirk and the original Enterprise crew to explore strange new worlds and new life forms. It was a show brimming with optimism about a 24th century where humanity had overcome its grievances and began working together in harmony with other alien races.
Exploring the galaxy is a dangerous affair, however. With dangers lurking every corner, there's no telling what the crew might encounter next. This led to some of the most terrifying episodes in the show that still freak out TNG fans after so many years.
Where Silence Has Lease (Season 2)
Both the Enterprise crew and the audience were subjected to psychological stress in this season 2 episode which found the Enterprise enveloped inside a spatial anomaly. The creep factor rose to 11 as the crew tried to find a way out, only to be hit with one illogical event after another.
Eventually they discovered they were experimental lab rats for an incredibly powerful alien known as Nagilum, who wished to study death in all its facets. This would have involved slaying one-third of the Enterprise crew in different ways, had Picard not threatened to self-destruct the entire ship.
Skin Of Evil (Season 1)
Most Star Trek episodes were all about adventure, excitement and some tension thrown in for good measure, but Skin of Evil changed the game completely. It was the first Star Trek episode to show real, actual repercussions when it came to the dangers of deep space exploration.
The plot centered around a creature named Armus which was literally the cast off accumulation of a mysterious species' evil thoughts and traits. It demonstrated its inherent evil by killing Tasha Yar with a "mere flick" of its power, then psychologically abusing the rest of the crew for its own amusement. Armus was truly frightening in a way past Trek villains were not.
Booby Trap (Season 3)
This popular season 3 episode pitted the crew against an enemy they could not see or fight against - a thousand-year old booby trap consisting of energy converters that drained the Galaxy Class Enterprise's energy reserves and converted it into lethal radiation. With time running out before fatal exposure, Geordi LaForge had to go under the gun to create an escape method.
The sheer tension of the episode ratchets up to unbearable levels when the shields finally drop, and the crew begins taking direct lashes of radiation. It ends in nail-biting, spectacular fashion when Picard utilizes an ingenious maneuver to escape the booby trap; one of his best moments.
Cause And Effect (Season 5)
One of the best TNG episodes ever written was also one of its most terrifying. It started out in shocking fashion, with the Enterprise exploding violently before the opening credits even show up on screen. From there, the audience is taken on a rollercoaster ride involving an Enterprise caught in a temporal causality loop which forces them to re-live the same catastrophic event over and over again.
Each time, a form of deja vu affects the crew which allows them to a little more about the incident than before. In a desperate bid to break the cycle, they must come up with a plan to warn themselves of the doom yet to come, or risk going through it for all eternity.
Identity Crisis (Season 4)
The concept of instinctual fear took on a whole new meaning with this episode centering around the mysterious deaths of several Starfleet officers who are compelled to return to an alien planet years after an away mission. Geordi LaForge was one of them, and he begins to experience the exact same symptoms.
It's revealed that a highly elusive parasite has infected every crew member, and has begun rewriting their DNA to turn them into one of the planet's local species. It's a terrifying episode that really hits its peak when LaForge re-enacts the mission on the Holodeck and pieces together the scary clues.
Genesis (Season 7)
This clever final season episode isn't just one of most fun to watch. It's also one of the most scary. Picard and Commander Data return to an Enterprise adrift in space and chaotic inside. The crew are missing, the hallways are dark, and there's no sign of an attack by an outside force.
They soon learn that the crew has begun to de-evolve at the cellular level, reverting back to different incarnations of other species, some more horrific than others. The show explores the concepts of humanity's instinctual primal fear built into our psyche through thousands of years of evolution.
Conspiracy (Season 1)
Nobody expected the rather happy-go-lucky first season of The Next Generation to take such a shocking turn towards the end. Over the course of the season, a minor plot thread was weaved into the story focusing around a mysterious conspiracy that threatened the existence of Starfleet.
Eventually, the conspiracy was revealed to be a reality when a parasitic alien species Picard and Riker managed to save the day by slaying a Starfleet Commander who's body acted as a host for a horrific parasite queen.
The Best Of Both Worlds, Part 1 (Season 3)
The Federation had faced down all number of lethal threats since its inception, but the dreaded Borg were cut from a different cloth. First encountered in season 2, they made their frightening return in the first of a two-part cliffhanger that bridged seasons 3 and 4.
The buildup of tension leading to the first big reveal of the Borg Cube was incredible, but it was just the start of the terror. The episode ended with Picard himself abducted by the Borg and turned into a nightmare Borg equivalent named Locutus. Audiences were left hanging with a cliffhanger that went down in history as one of the most shocking, and nobody knew whether Picard would survive, or if his time had come.
Schisms (Season 6)
Fear of hospitals and surgery is common among humans, as it cuts directly against our own survival instinct. Nobody likes the thought of being operated on, much less experimented on. That's exactly what happens in this terrifying season 6 episode featuring several crew suffering from inexplicable panic attacks.
They soon learn they're being taken in the middle of the night by an unseen force for experimental purposes. The fear reaches palpable, heart-pounding levels during a scene where the victims gather in the Holodeck to try and recreate the sights and (terrifying) sounds of the operating room that their subconscious minds have suppressed.
Night Terrors (Season 4)
Few episodes are about sheer, primal horror and fear like Night Terrors. It's the ultimate scary Next Generation episode both in story, and production. The psychological paranoia and fear among the crew begins to grow when they realize that they are being deprived of REM sleep, a necessary component to maintaining sanity.
As the crew begins coming apart at the seams, they start hearing things, hallucinating and going into full-fledged panic attacks. It's unsettling to say the least, but no other scene captures the horror better than when Doctor Crusher hallucinates a room full of dead cadavers sitting up in the Enterprise morgue.