The Enterprise is on a routine mission to chart an unusually dense globular cluster. Riker starts the morning feeling unusually tired, and arrives late for the morning briefing in engineering. After some technobabble discussion on how best to speed up the charting of the cluster, Data reminds Riker of his poetry recital in Ten Forward. At the recital, while most of the attendees are merely bored, Riker can barely stay awake, and falls asleep in the middle of Data's "Ode to Spot".
Riker sees Dr. Crusher about his fatigue, where he reports feeling constantly exhausted and on edge, despite getting a full night's sleep as far as he can tell. Crusher doesn't find anything physically wrong with him, and so sends him home with a recipe for a warm milk toddy and an invitation to return tomorrow if it doesn't help.
In engineering, Data is discussing his poetry with La Forge before they are interrupted when the sensors report an EPS overload in cargy bay 4. An emergency team is dispatched, but they find nothing out of the ordinary, leading La Forge to hypothesize that it was a sensor glitch caused by their recent modifications. Riker asks La Forge to wake him at 0700 the next morning because of his recent sleep troubles.
La Forge obliges, but Riker has no memory of falling asleep, and refuses to believe it's morning until he checks the clock. Suspicion mounts as further strange occurrences are noticed: Worf and Riker both have panicked reactions to ordinary stimuli, La Forge's visor starts randomly cutting out, and Data, of all people, finds that he has lost over an hour of time. La Forge observes that many of these events took place in the same cargo bay, and sure enough, they find a Negative Space Wedgie forming there from a deep layer of subspace that shouldn't be able to exist in normal space.
When Riker goes to Troi about his unexplained panic attack, she remarks that other crewmembers have reported similar problems, and decides to bring them all together to talk about it. They eventually go to the holodeck to try and recreate a repressed memory they all seem to share. The end result is a nightmarish operating table with a surgical arm in a dark room filled with a cacophony of alien clicking sounds.
More evidence appears indicating that random crewmembers are being abducted into another subspace dimension, where they are sedated and experimented upon. To make matters worse, the anomaly in the cargo bay starts expanding into a subspace rift. The senior staff come up with a strategy to stop the rift, but need a way to identify the exact dimension where it is originating. Since Riker has been abducted several nights in a row, he volunteers to take a homing device with him the next time it happens, which will allow the Enterprise to track him as he leaves.
Dr. Crusher gives Riker a stimulant in the hope that it will counteract the sedative used by the abductors. Riker goes to bed, and soon finds himself pulled into the other dimension. There, he finds himself on a surgical table being examined by robed aliens, alongside Ensign Rager, who was previously discovered missing. He feigns sleep until the Enterprise begins to close the rift, at which point he is able to grab Rager and escape through the rift while the aliens are distracted.
Despite resistance by the aliens, the Enterprise is able to close the rift once Riker makes it through, and the abductions cease. They believe the aliens had established a pocket of "normal" space in their laboratory in order to experiment on the crew, and the rift in the cargo bay was their attempt to create a pocket of their own space in the Enterprise's universe. Data hypothesizes that the aliens may simply have been curious, but Riker strongly disagrees
- Alien Abduction: And not the friendly kind.
- Aborted Arc: Originally this episode was meant to begin a story arc dealing with the unidentified aliens. However, due to production issues, the crew were ultimately unsatisfied with the final product, leading to plans for further episodes being scrapped, resulting in the Ambiguous Ending listed below.
- Ambiguous Ending: Much is left unanswered by the end. Who were the aliens? What did they want with the crew? Will they ever try to enter our universe again? The tone of the episode implies a sinister answer to all of these questions.
- Another Dimension: Subspace has always been among the most loosely-defined fictional concepts in Star Trek, but this episode takes it to a new level with La Forge's revelation that it contains an infinite number of domains which, based on Riker's experience, have (or at least can have) their own spacetime dimensions and intelligent life.
- Body Horror: The aliens' experimentation starts out fairly unobtrusive, but things start to get nasty when one crewman is returned with his blood turning into a liquid polymer. He doesn't survive. Dr. Crusher also discovers that Riker's arm has been severed and then surgically reattached.
- Call-Back: Crusher introduces Riker to an insomnia treatment (warm milk) favored by Picard's Aunt Adele.
- Giftedly Bad: Braga deserves credit for drafting the "Ode to Spot," a poem which has been written by a being without emotions, and which simultaneously meets flawless technical criteria and is hilariously dull and terrible, forcing the entire crew to listen, straight-faced and bored, to try to protect his nonexistent feelings.
- Hesitation Equals Dishonesty: Data lampshades this when asking Geordi his opinion on Data's poetry. Since he has no feelings to protect, Data prefers that he were honest.
- Hyperspace Is a Scary Place: Or "Subspace is a Scary Place" in this case. An infinite honeycomb of infinite spaces, some of which are apparently capable of supporting life with an at best loose code of ethics, who will take you away in your sleep and do all sorts of ghastly things to you to serve their unknowable purposes, and potentially destroy your ship in the process. Enterprise learns this the hard way, and warns the rest of the fleet not to repeat their mistakes.
- The Insomniac: Riker can't seem to get any rest no matter how much he sleeps. It turns out this is a result of the subspace aliens' experiments.
- Kidnapped While Sleeping: Several Enterprise crew members are abducted from their rooms while sleeping and taken through a subspace rift into an alien laboratory. Once there, they are experimented on by the aliens.
- Laser-Guided Amnesia: Courtesy of the subspace aliens. It's not complete, however: see the Trauma Button entry. Some of the affected crewmembers use the holodeck to recreate their repressed experiences from bits and pieces of what they can remember, and the results are nightmarish.
- Missing Time: Data loses an hour and a half while in the troublesome cargo bay. It transpires he was abducted by the subspace aliens.
- Negative Space Wedgie: The aliens try to intrude their way into the Enterprise's universe via a subspace portal, nearly destroying the ship in the process.
- Scifi Writers Have No Sense Of Scale: Globular clusters are dense clusters of stars in the galaxy's halo, the nearest (Messier 4) being around 7200 light years away from Earth. Meaning that unless a wormhole was involved, it would have taken the Enterprise at least seven years to get there even at full warp.
- Sequel Hook: A subspace entity of some kind is able to evade containment and flees into the unknown. Once they have the situation under control, Enterprise recognizes that whatever they encountered was at the very least not friendly, and warn Starfleet to take precautions as they expect this won't be the last time they try to break into the universe.
- The Stinger: Something from the subspace universe escaped into our own and off the Enterprise before it could be contained.
- Trauma Button: Innocuous objects begin evoking unsettling emotional responses in the Enterprise crew, one of the first clues that something is going on. Riker reflexively flinches away when Dr. Crusher moves a medical scanner towards his face, and Worf is so disturbed by Mr. Mot's scissors that he walks out on his haircut.
- Trailers Always Spoil: Much to the consternation of writer Brannon Braga, the "next week on" gives away the Alien Abduction plot, which is a mystery until the 5th act in the show proper.