The good chief got a face full of exploding plasma conduit, which has left him with an easily curable bout of radiation poisoning. He'll be fine, but Bashir tells him to take it easy.
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 while 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 aren't happy with the minor information they've obtained on the Dominion. Especially since they lent them one of their cloaking devices. 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, is O'Brien. Who vanishes.
Turns out there's a temporal disturbance bouncing around the station. And the residual radiation O'Brien got when the conduit exploded has interacted with this, 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 good old fashioned 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. And down come the instigators of the fight O'Brien saw during his last time-shift. The Klingons have come to pick a fight with the Romulans.
The fight occurs as it did in his previous time-trip. His younger self assists him and vice-versa. 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. Dax meanwhile may have found a cure.
Sisko and Odo find evidence of a modified food replicator that was jury-rigged into a transporter. Which beamed the weapon into the conduit and killed O'Brien. Though the crisis appears averted, O'Brien is still nervous as the time approaches...and you guessed it, 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.
His next time-jump is not much funner. 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 stations 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. Although to be honest, Klingons = violence almost a hundred percent of the time anyway...
- 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.
- 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 an 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.
- 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.
- 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.
- My Friends... and Zoidberg: Odo delivers this when talking to Sisko about the surveillance device planted in the bulkhead.Odo: Don't worry. I plan to investigate the Klingons, the Bajorans, Quark, the visiting Terrelians
Sisko: You think Quark had something to do with this?
Odo: I always investigate Quark.
- Oh, Crap!: O'Brien and Quark when they see the duplicate O'Brien on the Promenade.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.
- 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.
- 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.