The Enterprise locates a missing science vessel, finding just one surviving crewmember aboard -- a Betazoid in a catatonic state. The rest of the crew seems to have killed themselves and each other following a string of unexplained hallucinations. When the same symptoms begin to appear on the Enterprise, they attempt to flee, only to find their ship has become trapped in a Tyken's Rift, an interstellar phenomenon that is draining the ship's energy and disabling its engines. The crew must find an escape and cure their hallucinations before they're all driven mad.
As I said, you won't find anybody associated with Star Trek: The Next Generation willing to defend this episode. Director Les Landau won't even talk about it, noting only that it had something to do with Troi floating in space. Visual effects supervisor called the realization of that Troi nightmare "horrible." Producer Rick Berman thought the episode was hard to follow, and head writer Michael Piller blamed the horrible pace. And they're all right. But personally, I don't think this was even the worst episode of the season, never mind one of the worst for the series. So I'll step in with at least a partial defense.
The core idea here, to do a suspenseful horror episode, is a good one. (In fact, the series would try again in a later season to better effect, using an alien abduction premise.) Indeed, a few of the moments here are absolutely effective, such as Dr. Crusher's creepy encounter with the Brattain corpses in the ship's morgue (which Gates McFadden plays wonderfully without overacting). Riker finding snakes in his bed is unsettling too (and again, played reasonably well by Jonathan Frakes). There are a few other interesting, tangential ideas too, such as the notion that it's still possible to communicate telepathically with a catatonic person.
But the good moments are overshadowed by bad ones. I'm not even sure what Picard's turbolift hallucination is meant to be; one moment he's flying upward, and the next it seems like the ceiling is lowering on him... I think? Does the story really earn the moment where Worf is about to kill himself? And then there are the guest stars, who have an awful lot of weight put on their shoulders. One-off characters start to break down before any of our main characters do, and each one of them is horribly overplayed by a desperate young actor trying to get a big break.
Though yes, of course, the worst element of all is the ill-conceived "Troi flies through a tunnel" idea. For starters, it's supposed to be a nightmare... but most people associate flying with very pleasant dreams. Plus, Troi is always looking for someone (using terrible dialogue), not running from someone... again a reversal of the normal conventions of nightmares. Then there's the fact that Troi rather implausibly concludes in the final act that this nightmare must be an alien communication, and coincidentally realizes that the "one moon circles" repeated in the nightmare is a distress signal requesting hydrogen. That feels like it's putting an awful lot of stock in a dream, when dreams are inherently nonsensical.
It's also a bad idea to tie the hallucinations to a lack of REM sleep. I can understand why the writers wanted to connect to a real world thing rather than yet another made-up sci-fi disease, but it's problematic to ask actors to convey fatigue when they're on a time table. Michael Piller revealed that this episode ran more than 9 minutes long in its first cut, and had to be gutted to reach the final running time. Not only were the actors speaking slowly to demonstrate their fatigue, they were all working on their first episode back after a long Christmas break; Piller thought the latter in particular had them all a bit off their A game.
One person who did bring his A game was composer Ron Jones, who wrote a truly unsettling score for the episode. But after past problems relating to an absence and a technological malfunction, this episode was probably his "third strike." Jones brought in an actual 16-voice choir to supplement the orchestra for this episode, an expensive decision. And he wasn't 100% sure at the recording session how he was going to use them. He recorded takes of them singing dissonant chords, and others of them actually chanting "eyes in the dark" along with Troi's nightmare aliens. It all seems a bit crazy, but the finished product, which can be heard on The Ron Jones Project soundtrack album, is brilliant. Yet in the episode itself, the volume on the music is turned down so low you can hardly hear it. Clearly, Rick Berman didn't like it, and I believe this was the moment when he decided formally to shop for a new composer to replace Ron Jones.
- The other Federation ship, the Brattain, was meant to be named for Walter Houser Brattain, the inventor of the transistor. Unfortunately, the name is misspelled "Brittain" on the ship's hull. (They at least get it right on the computer displays on the set.)
- Miles and Keiko appear briefly in this episode, to have a REM fatigue-fueled quarrel. But as the writers really have to protect the characters from looking bad, the argument doesn't even involve so much as a raised voice.
- If it's questionable why they'd bring in Miles and Keiko for such a small part, it's truly mystifying why they'd bring in Guinan. Sure, the moment where she fires off a 1980s-style action movie quip (after firing off an enormous gun) is pure badass fun, but that upsets the tone the episode was going for. And neither Whoopi Goldberg nor the writers seem interested in portraying Guinan as being affected by the same fatigue as everyone else.
- Marina Sirtis had long been lobbying for Troi to get more action-oriented scenes, and claimed that here, it totally backfired on her. She spent an entire day suspended on wires to film Troi's dream sequences, and she is deathly afraid of heights.
- Speaking of Troi, I believe in this episode she is seen wearing every outfit in her wardrobe but one (the dark blue dress). I suppose this was to show the passage of time in the episode.
- Picard tells Data about watching the deterioration of his grandfather's mental faculties, to a condition that sounds a lot like Alzheimer's. It's a weirdly downbeat note for Star Trek to imply either that the disease is still uncured in the future, or that some other sci-fi version of the same thing just sprung up to plague humans in its place. Though the tale is at least consistent, in that it informs Picard's willingness to help a similarly afflicted Sarek in a wonderful previous episode.
- When they destroy the rift at the end of the episode, all the ship's systems immediately come back online. But when you drain a battery to almost empty and then stop the drain, it's not like it's instantly recharged. Future tech, I guess.