The Man Trap (TOS) The Original Series thought it would start out right. The very first episode ever to be broadcast, "The Man Trap" features a shape-shifter that can be anyone feeding on the crew of the Enterprise. If the suspense and screaming at the characters not to go behind the rock alone don't do it for you, one look at the creature's true form will.

The Enemy Within (TOS) A transporter accident unknowingly splits Kirk in two: a good and an evil side. (You can tell which one is evil because of the eyeliner and the screaming.) As each side becomes increasingly unstable, a confused crew tries to figure out which is which and how to put them together again. It's Dr. Jekyll and Mr. Hyde in space.

Wolf in the Fold (TOS) A vacation turns into a mystery when Scotty's found with a murdered girl with no memory of what he was doing at the time, the murder weapon clutched in his hand. The body count starts rising and it looks like Scotty's to blame, but digging deeper only brings forth a creepier explanation. The disembodied voices will send chills down your spine.

Night Terrors (TNG) Perhaps best known as the episode in which the dead bodies sit up and stare at Dr. Crusher, "Night Terrors" leads the way for Next Generation. You'd think if they found a derelict ship floating about with everyone onboard murdered, they'd get the hell out of there. But they don't, and the crew loses the ability to tell the difference between what's real and what's only in their heads. Tell me this one doesn't make the hair on the back of your neck stand up.

Schisms (TNG) What starts out as a routine science mission starts to go subtly awry. People start losing large chunks of time with no memory of what has happened in that time period, and the crew seems to be experiencing a mass nightmare of being trapped and experimented on. But is it really a dream? And the clicks, the clicks …

Frame of Mind (TNG) Commander Riker is performing a crazy person in a play. Or is he? Perhaps he's really been a crazy person all along, and his life on the Enterprise is an elaborate hallucination. Or perhaps he really is on the Enterprise, and the craziness is a hallucination. By the end of the episode, you won't have any idea which way is up and might suspect you've gone a little insane yourself.

Genesis (TNG) Does messing with T-cells ever result in anything good? Data and Picard go out to retrieve a mis-aimed torpedo and return to find the ship adrift and the crew de-evolved into a mix of truly horrific creatures that I'm not actually sure are anywhere in our genetic line. If the psychological horror of knowing you could be next while avoiding the deadlier members of the crew doesn't get you, there's always Barclay in his half-spider form to jump out at you.

Whispers (DS9) Something's wrong. It's just little things, but it starts to build up. No one's acting quite normal, and when O'Brien starts looking into it, he finds that he's been locked out from logs he should be able to access, that he's been kept from doing his job by purposeful sabotage, and that no one's on his side. This one's got a nice twist at the end that would do the Twilight Zone proud.

Distant Voices (DS9) After a telepathic attack, Julian wakes up to find the station deserted and rapidly falling further into disrepair. He's also aging at an accelerated rate and hearing voices no one else can hear, whispers that sound almost familiar. As a dangerous presence starts picking off his friends, Julian must fight for his life—in a different way than you'd think.

Empok Nor (DS9) Deep Space Nine—already the darkest of the Star Treks—gives us a good old fashioned tale of a haunted, well, station, in this case. Deep Space Nine needs parts that have to be scavenged from a nearby abandoned Cardassian space station, but it turns out to not be as abandoned as they had thought. In fact, it's the sort of place that might allow some people to act on their darkest instincts.

Darkling (VOY) Moving on to Voyager, the good ol' EMH has decided he's in need of a personality lift to better help him relate to his patients. Nothing could possibly go wrong when you mess with your own programming, right? But the historic figures he tries to model himself off all have a dark streak, and maybe he likes being evil just a little too much.

The Haunting of Deck Twelve (VOY) Here's an episode that's upfront about its motives. Voyager needs a complete power shutdown, leaving Neelix in charge of the Borg children, so he spins them a tale about an incident not too long in the past that resulted in part of deck twelve being blocked off. It features everything you want in a good ghost story: things that go bump in the night, creepy shadows, and a monster that's willing to kill.

Impulse (ENT) Seriously, one day Starfleet will put out a memo that says “Warning: Derelict ships may contain hazards.” Enterprise gets a bit of a pass, though, technically happening before everyone else. Still, it’s no joking matter. Zombie Vulcans really ruin your day. See, the thing about Zombie Vulcans is that they’re still Vulcans, and therefore smarter than you.