Elsewhere, a Romulan contingent is headed for the station...at the same time a damaged Klingon freighter is there. Knowing that the two species mix like fire and oil, Sisko advises Odo to keep them away from each other.
Taking Bashir's advice, O'Brien is relaxing at Quark's, trying to explain the appeal of darts, when he suddenly finds himself on the promenade in mid-throw. Glancing over at the adjacent catwalk, he sees...himself, talking with Quark about a Klingon damaged holo-suite. Flashing back to Quark's, he passes out on the spot.
In sick-bay, Bashir fixes him up and assures him that his vision was just a side-effect of a Techno Babble deficiency in his brain. He's not convinced.
Sisko and Kira meanwhile are dealing with the naturally hardass Romulans. They want the intelligence that the Federation promised in return for their loan of the Defiant's cloaking device, and they aren't happy with what they receive. The ambassadors start interrogating Sisko and Kira, even going so far as to question if Odo is a spy.
Meanwhile, O'Brien is wandering the promenade when Quark approaches him. His holo-suites have been damaged by some rowdy Klingons. In the middle of this discussion, O'Brien realizes this has happened before. When he had his mysterious vision. And indeed, on the adjacent catwalk, there's O'Brien, who vanishes just like before.
Turns out there's a temporal disturbance bouncing around the station. The residual radiation O'Brien got when the conduit exploded has interacted with it, randomly sending him into the future and back again. And he's about to go again. This time he's in Quark's, square in the middle of a massive Bar Brawl. After giving his other self a little assistance in the fight, he returns to Sisko's office and passes out again.
The news ain't good. He's fine for now, but the damage all this time-shifting is doing is adding up. If they can't fix it, he's gonna die.
After Kira has a blow-up with the Romulans, O'Brien is back at Quarks playing darts with Bashir. They've forbidden the Klingons from coming to the bar to prevent the brawl that O'Brien saw, but several come down from the holosuites and immediately pick a fight with the Romulans, instigating the brawl. The fight occurs much like it did in his previous time-trip, but this time O'Brien is ready and does better in the fight than he saw himself do the first time. As security breaks up the tussle, he heads for another trip in time. This time it's not just some random event. He watches himself get fatally shot by a phaser beam from a wall conduit.
Investigating the corridor where the event is set to occur, Sisko and Odo can find nothing odd about the conduit. They station a camera in the corridor just in case. But then Kira announces that she moved the Romulans quarters to Section 47, the same corridor where O'Brien saw himself murdered. Soon, the crew detect that a device was covertly beamed into the conduit.
Sisko and Odo figure out that a food replicator was jury-rigged into a transporter to do the transport work. The modifications will be the only clue about who did the work. Though the crisis appears averted, O'Brien is still nervous as the time approaches when he saw himself die. In the moment, he's sent on another time-shift. Where he finds his own corpse in the sick-bay. Bashir pops into the room, telling him to tell past-Bashir to perform a basilar arterial scan that will save past O'Brien. He returns to the past and does just that.
Odo gets the proof he needs that the Klingons are actually Klingon spies. He rounds them up and threatens to let it be known that their mission was a failure, thus incurring the wrath of Klingon Intelligence, unless they fess up and help him. They consider his offer.
In O'Brien's next jump, he finds himself, his other self and a throng of people in an escape pod. As they leave, DS9 explodes behind them and the wormhole collapses. He doesn't have any evidence of who or what caused the station's destruction. But he intends to find out. He wants to be sent into the future on purpose this time, so he can save the station. Bashir fixes him up with a Techno Babble time travel device, and sends him on his way.
The answer soon becomes clear as O'Brien #1 and O'Brien #2 enter ops. The destruction was caused by a Romulan warbird that's been cloaked outside the station. And it gets worse. The radiation has caught up with O'Brien #1. He's done for. So he gives O'Brien #2 the device and sends him back to warn Sisko.
Turns out the Romulans were there to destroy the wormhole, thus ending the threat of the Dominion. And since Bajor and the Federation wouldn't allow it, they'd have to destroy the station too. The Romulans are escorted off the station, and O'Brien settles into his same-but-new life.
- Bar Brawl: Drunken Klingons + drunken Romulans = violence.
- Blackmail: Odo uses his favorite tactic to try to convince the Klingon spies to help him or else he'll communicate their failure to Klingon Intelligence.
- Brick Joke: At one point, Quark suggests that O'Brien use his future knowledge at the dabo table. O'Brien ends the episode by telling Quark "Dabo" just before someone at the table wins.
- Butt-Monkey: Wouldn't be an O'Brien episode without it. This particular case comes with a grand total of three time travel related deaths.
- Cutting the Knot: The Romulans forego their usual subtlety by launching an outright assault against DS9 to destroy both it and the entrance to the Wormhole (making it look like the Wormhole's "accidental" collapse destroyed the station instead of the Romulans).
- Deadpan Snarker: Bashir, when O'Brien tells him about the hallucination.Bashir: Well, you do have one problem. If all you can hallucinate about is Quark's maintenance problems, you have a sadly deficient fantasy life.
- Discovering Your Own Dead Body: By the end of the episode, O'Brien — or, at least, the O'Brien the episode ends with — has witnessed two alternate versions of himself die and come upon the sheet-covered corpse of a third. He's understandably somewhat freaked by this.O'Brien: I've had a few brushes with death in my career, but... there was something about watching myself being killed. Feeling my own neck for a pulse that wasn't there.
- Expendable Alternate Universe: Future O'Brien ends up dying a few times over, but nobody cares because present O'Brien is A-OK and prevents his own death. Subverted, however, when present O'Brien is the one to die (of radiation poisoning), and future O'Brien goes back to the present to take his place for the rest of the series. Future O'Brien is understandably bothered about all this, but Bashir just handwaves it, asserting he's the same O'Brien with a few hours of extra memories.
- Explosive Instrumentation: What kicks off the plot by striking O'Brien before the episode starts.
- Failed a Spot Check: O'Brien's time-shifting is determined to be caused in part by a quantum singularity somewhere in the area. Somehow, not one person among an experienced Starfleet crew even attempts to make the connection between this and the Romulans visiting the station, who are the only mentioned race in Star Trek to use quantum singularities in their ships, which can also cloak.
- Five-Second Foreshadowing: When present-day O'Brien meets his future self for the last time, the latter is confused by the fact the former is suffering from the radiation sickness (thanks to the time-jump) and he isn't. This is dismissed with a Played for Laughs grumbling over how the Timey-Wimey Ball works. The audience is primed to assume that the reason is simply because once O'Brien completes the mission and returns to the present, Bashir will cure him, so there won't be any radiation to still be affecting O'Brien in the future. But it turns out the real reason is because past O'Brien is going to die from it, and non-irradiated future O'Brien will take his place.
- Foreshadowing: The Romulans have concluded the Dominion is a serious enough threat to warrant attacking Deep Space Nine and collapsing the Wormhole. While the Romulan military's mission fails thanks to O'Brien, the Romulan Tal Shiar will take their own crack at the Dominion very soon...
- Futureshadowing: O'Brien repeatedly sees what is to come, including his own deaths.
- Gilligan Cut: As Kira puts it...
- I Know A Guy: Odo starts giving a long-winded explanation of how he found out about the device, saying he spoke to a friend at Starfleet Intelligence who put him through to a Klingon who's out of favor with Gowron, until Sisko tells him to just get to the point. Odo says that this was just to show how good he is at investigating.
- If I Do Not Return: O'Brien tells Bashir that he has a Video Will for Keiko in case he doesn't survive the time-trip.
- Knows a Guy Who Knows a Guy: How Odo figures out what the Klingons are up to, though the explanation annoys Sisko.Odo: But then I contacted a friend at Starfleet Intelligence who used to be assigned to the Federation Embassy on the Klingon homeworld. He put me in contact with a former Klingon operative who's out of favor with the current administration. This former operative sent me a series of reports—
Sisko: Odo, cut to the chase.
- Know When to Fold 'Em: When Sisko confronts the Romulan delegates with evidence of their impending attack on the station (thanks to O'Brien's time travel shenanigans) and tells them he has the station's weapons locked on the energy signature of their Warbird, they simply stand up and leave without protest.
- Make It Look Like an Accident: The Romulans' plan is to destroy Deep Space Nine with a cloaked Warbird, and make the whole disaster look like an accidental collapse of the wormhole. This would keep the Dominion on their side of the galaxy, and kill any witnesses in the process.
- Obfuscating Stupidity: The three Klingons spend their time drunkenly picking fights and wrecking holosuites but are actually highly trained spies on a covert mission.
- Oh, Crap!:
- O'Brien and Quark when they see the duplicate O'Brien on the Promenade, to which the Ferengi quickly makes himself scarce.Quark: I think my holosuites can wait. It looks like you have bigger problems.
- Then a much bigger one when O'Brien flashes to the future and sees the station explode.
- O'Brien and Quark when they see the duplicate O'Brien on the Promenade, to which the Ferengi quickly makes himself scarce.
- Only Sane Man: Mercifully avoided. Quark himself sees the "other" O'Brien while talking to the "original" version.
- Powered by a Black Hole: Exploited: the crew are able to locate the cloaked warbird by hunting for the mass signature of its drive singularity.
- Sci-Fi Writers Have No Sense of Scale: The quantum singularity they detect that's causing the problems is only two kilometers from the station. For comparison the station is one and a half kilometers across and the cloaked Romulan Warbird causing the issue is a kilometer long; it's astonishing there wasn't a collision.
- Ship Teasing: The two Romulans insinuate that Odo is in love with Major Kira. Kira finds the idea impossible, and Odo agrees with her.
- Spanner in the Works: The Romulan plan to destroy DS9 and the wormhole would've worked if not for the Techno Babble radiation hitting O'Brien and the ensuing time jumps.
- Temporal Sickness: The radiation that makes O'Brien jump in time causes more damage to him each time. Two versions of him eventually die from it.
- Timey-Wimey Ball: Lampshaded by the two O'Briens when the past one is suffering from Temporal Sickness but the future one isn't: "I hate temporal mechanics!"
- You Can't Fight Fate: Mostly averted. They fail to prevent the Bar Brawl, but they do avoid O'Brien's deaths and the station's destruction. And even when the bar brawl comes to fruition, O'Brien avoids getting sucker-punched like he did the first time.
- You Have Failed Me: Odo threatens the Klingon operatives with the thought of their superiors pulling this on them if they find out they were caught, and offers to let them go in exchange for a full confession.