Guinan is introducing Worf to the wonders of prune juice when the ''Enterprise'' comes upon some sort of space-time disturbance. Suddenly, a ship emerges - the ''Enterprise''-C, displaced 22 years in time. And it has survivors.

Panning back to the bridge of the ''Enterprise''-D, things are...different. The lighting is darker, the design a bit more sinister, the uniforms are a slightly different design and Wesley is a full member of Starfleet - and holy crap, is that Tasha Yar standing there where Worf ought to be? Worf's absence is easily explained: the Federation has been at war with the Klingons for over 20 years, a war which they are now on the brink of losing. They desperately need any ship they can get, and the ''Enterprise''-C, though badly damaged, looks repairable.

They bring the survivors on board, including the moderately injured Captain Garrett. She tells Picard and Dr. Crusher that they had been responding to a distress call from a Klingon outpost when they were set upon by four Romulan Warbirds and were moments from destruction when they fell into the rift. It's a pity, really - just think what beneficial effects a Federation rescue of a Klingon base might have had on the negotiations then taking place. Why, 20 some years of devastating war might well have been averted!

Alone of the crew of the ''Enterprise'', Guinan has noticed that something is Wrong. She talks to Picard about it, but isn't able to give him anything more definite than that this isn't what's supposed to be happening, and implores him to send the ''Enterprise''-C back through the rift to where it belongs. Picard is understandably reluctant to send 124 people into certain death based only on a few cryptic remarks from his bartender, but Guinan begs him to trust her. And then the Klingons turn up.

Meanwhile, Tasha has been liaising with the acting second in command of the ''Enterprise''-C; Lieutenant Junior Grade Richard Castillo, trying to get the older vessel combat ready once more. The two of them clearly like each other, even all the very strange looks Guinan keeps giving her are a little disconcerting. Picard finally decides to send the ''Enterprise''-C back where it belongs, on the logic that even if it is a suicide mission, Klingons have an awful lot of respect for people who die in battle, and they're all just going to get killed anyway when the present day Klingons turn up. Which they promptly do.

In the ensuing battle, both ships are badly damaged and Captain Garrett is killed by a piece of shrapnel. Tasha confronts Guinan about the aforementioned strange looks, and Guinan admits that in the "correct" timeline, she died horribly and pointlessly. Upon hearing this cheerful news, Tasha decides to transfer to the ''Enterprise''-C and take her chances with the Romulans, where at least her death might make a difference. This couldn't possibly have any consequences down the road at all.

Those pesky Klingons still won't go away, though, and as the ''Enterprise''-C limps back towards the rift, the ''Enterprise''-D devotes itself wholly to defending its doomed predecessor. Harried by three Birds of Prey, and with a warp core breach imminent, it looks like the end for both ships. Just as the ''Enterprise''-D is about to be destroyed, the ''Enterprise''-C makes it into the rift-

...and everything returns to normal. The episode ends with Guinan glancing about a well-lit, happy Ten-Forward, and she sits down [[CrowningMomentOfHeartwarming to ask Geordi about Tasha Yar]].

!!Tropes:

* AbsenteeActor: Marina Sirtis (Counselor Troi) only appears in the two short bridge scenes on the "regular" Enterprise - one before and one after the main plot of the episode - and has no dialogue.
* AnyoneCanDie: The best thing about an AlternateTimeline episode.
* BadPresent: Or BadFuture -- it is a BadFuture story in everything but the fact that bad alternate time is the present from the perspective of the main characters.
* BadassBoast: "Let's make sure history never forgets... the name... '''Enterprise'''."
* {{Blooper}}: In one of the most glaring bloopers of the series, the final scene set in the 'correct' universe features Geordi wearing the alternate timeline style uniform.
* CoolStarship: The ''Ambassador-class'' ''Enterprise-C''. Notable in that the Ambassador only made two other appearances in the franchise and it remains an extremely popular ship in the fandom.
* FacingTheBulletsOneLiner: The ''Enterprise'' is crippled, with no chance of winning the battle. The Klingons offer to let the ''Enterprise'' surrender.
-->'''Captain Picard:''' That'll be the day.
* FixFic: Denise Crosby left the series unexpectedly while the first season was being filmed, which meant Tasha Yar had to be written out. Many viewers criticized [[Recap/StarTrekTheNextGenerationS1E22SkinOfEvil Yar's demise]] as being abrupt and pointless. When Crosby returned for this episode, the writers got a chance to give her a more heroic death. This is [[LampshadeHanging lampshaded]] in the dialogue between Yar and Picard, when he says that instead of having a "senseless death" she wants her sacrifice to "count for something".
* {{Foreshadowing}}: The Bad Future Enterprise-D is destroyed in the exact same way as the Enterprise-D we've been watching through the show will be: [[spoiler: Klingon Birds of Prey damage the warp engine, which causes a warp core breach.]] In fact, it's so precisely identical, the same panel explodes and the core starts leaking from the same spot.
** In fact, Geordi's dialogue is almost lifted word for word come Generations, with just the time until explosion changed between the two versions.
* ForWantOfANail: The whole premise of the episode; the ''Enterprise''-C turns out to be a very important nail indeed.
* GettingCrapPastTheRadar: And not even trying very hard. Guinan tries to talk Worf into seeking... [[YouNeedToGetLaid companionship]] from other members of the crew. Worf states that human women are far too fragile, and that he would require a Klingon woman for... [[InsistentTerminology companionship. ]]
* GrowingTheBeard: One of the key episodes that made Season Three so memorable.
* HeroicSacrifice: The original fate of the ''Enterprise''-C, fighting four Romulan warbirds in defense of a Klingon colony before the Klingons and Federation were allies. Also the fate of the {{Bad Future}}'s ''Enterprise''-D.
* HeyItsThatGuy: The surviving ''Enterprise''-C bridge officer, Lt. Castillo, is played by Christopher [=McDonald=]!
* MildlyMilitary: The fact that this trope is {{Averted| Trope}} is one of the earliest indicators to the audience that something is off. All of the crew carry phasers aboard the ship, the lighting is dimmed for a darker mood, the ramp leading to the back of the bridge has been replaced with steps, fewer chairs on the Bridge for officers to lounge in ([[NumberTwo Riker]] now stands behind the railing instead of sitting at the Captain's side), the replicators produce standardized military rations, the ship doesn't have a counselor on the bridge - Troi doesn't appear in the Bad Future at all - and the ''Enterprise'' is even [[InsistentTerminology repeatedly referred to]] as a "battleship" instead of a "starship". The ''Enterprise''-C, meanwhile, is referred to as a cruiser. Even the uniforms are slightly different, now having a closed collar to make the final frontier just that ever bit less friendly.
** There's also the interaction between Picard and Riker. Riker is not "Number One" in this timeline, but is "Commander." Picard is noticeably more emotionally removed from the other officers, giving the atmosphere on the ship more of a tense feeling.
* MundaneMadeAwesome: Prune Juice... ''A Warrior's Drink!''
* NegativeSpaceWedgie
* OhCrap: [=LaForge=] delivers a well-warranted one. Doubly warranted if you consider that the ''Enterprise's'' plasma coolant is [[BodyHorror horrifically corrosive]] to organic matter.
--> '''[[TheEngineer LaForge]]:''' "Coolant leak! We have a ''coolant leak!'' Estimate two minutes until a Warp Core Breach!"
* RippleEffectIndicator: Worf departs for the bridge. Time Ripple ensues, and we cut to Tasha Yar (having died previously on the show) on the bridge in Worf's place. Once the timeline is restored, Worf is back where he should be.
* RippleEffectProofMemory: Guinan only, and [[DownplayedTrope downplayed]] at that: She doesn't seem to know '''exactly''' what's wrong with the timeline ("I know it's the same bridge; I also know it's ''wrong!''"), but she had a good idea how to fix it.
* SacrificialLion: One for each space battle shown: Captain Garret and Commander Riker.
* SetRightWhatOnceWentWrong: The ''Enterprise''-C's mission. The crew of the ''Enterprise''-D set forth to help them and protect them until they can go back.
* WhatCouldHaveBeen: If not for cost and time constraints, the writers originally planned for most of the TNG crew's deaths in the BadFuture to happen on-screen - Wesley would end up decapitated and Data would be electrocuted. Instead, only [[NumberTwo Riker]] is shown to die.
** The ''Enterprise''-C is based on a model originally conceived as a regular 'guest' Starfleet ship type that had been planned to be made for the pilot. It was also somewhat simplified from the original design for cost reasons, originally being sleeker.
* WhatHappenedToTheMouse: Whatever became of Tasha Yar after going back into the past? This question gets answered later on in the show.
** Meanwhile, no mention is made in the BadPresent of Mr. Worf, who quietly disappears between scene changes once the NegativeSpaceWedgie appears (the last we see him is when he departs for the bridge, we won't see him again until they SetRightWhatOnceWentWrong, when he is seen on the bridge as if had just arrived).
*** The novel ''Q Squared'' provides part of answer to this: Worf is rescued by his own people and grows up "standard" Klingon. The treason charge isn't slapped on himself and Kurn since, with Mogh as an active House, they don't make quite as convenient scapegoats. Worf becomes captain of a warship and a celebrated destroyer of Federation ships. The novel also explains Troi's disappearance from the episode as well: the Betazoids had been wiped out by the Klingons.
**** Unnecessary, since there's no need for a ship's counselor on a militarized warship anyway.
** The shooting script had indicated that it could have been Worf on the other end of the commline, instead of a random Klingon. One wonders why they changed their mind.
* WhatYouAreInTheDark: Inverted. If the ''Enterprise''-D is successful in helping the ''Enterprise''-C return to their time, the crew of the ''Enterprise'''-D will have no idea what they did and what it meant for the Federation. They still do it, because it's the right thing to do. Although, back in the in fixed timeline, Guinan knows and later tells Picard.
* YouAlreadyChangedThePast
* YouShallNotPass: The ''Enterprise''-D's HeroicSacrifice to allow the ''Enterprise''-C to get back to her own time.
-->'''Captain Picard:''' Attention all hands. {{As you know}}, we could outrun the Klingon vessels. But we must protect the ''Enterprise''-C until she enters the temporal rift. [[LetsGetDangerous And we must succeed.]] Let's make sure history never forgets... the name... ''Enterprise''. Picard out.
** And of course, once the timeline is restored, the final fate of the ''Enterprise''-C, destroyed after taking on four Romulan warbirds in defense of a Klingon colony. Never forget the name ''Enterprise'' indeed.