Visionary: O'Brien becomes unstuck in time.
O'Brien comes around to find that he's been knocked on his arse by an exploding conduit. Sisko tells him he's on light duties until he recovers. Meanwhile a Romulan delegation are coming aboard, and some Klingons are also around because their ship is busted. Sisko is concerned the Klingons might cause trouble. O'Brien attempts to introduce darts to Quark's bar. Quark attempts to try it out by throwing the whole lot and skewering Morn. When O'Brien goes to demonstrate, he suddenly finds himself on the Promenade, watching himself bitch at Quark about the Klingons damaging the holosuites. As the two O'Briens notice each other, he finds himself promptly back in Quark's bar again and collapses.
The Romulans think Odo might know something about the Dominion's plans because he's a changeling. They're a bit grumpy because despite providing a cloaking device for the Defiant, the Federation hasn't provided very much in the way of info on the Dominion.
O'Brien encounters Quark, who says that the Klingons have damaged his holosuites. Then they both notice another O'Brien standing on the other side of the Promenade. During the ensuing discussion in Sisko's office, O'Brien finds himself amidst a barfight in Quark's, and saves himself from a Klingon.
Bashir says if he keeps time shifting, the cumulative damage is likely to kill him. Kira says that the Romulans are demanding more access to the Defiant sensor logs and so on. The Romulans attempt to debrief Kira re the time the Dominion captured the Defiant, and... yeah, doesn't go well.
Bashir and O'Brien play darts in Quark's bar while waiting for the bar fight. The Klingons swagger through and confront the Romulans. Cue barfight. Odo's called in. O'Brien manages to overpower the Klingon himself, but then timeshifts again and watches himself get killed from a panel discharge. NO! Don't touch yourself! Blinovitch limitation effect!
He wakes up in the infirmary back in his own time, where he tells Bashir that in a few hours he's going to be killed. Dun dun duuuuuuuuuuuuun!
He takes Sisko and Odo to the panel in question. Odo carefully opens the panel but finds nothing. They reason that whatever killed O'Brien hasn't been placed there yet, and decide to set up surveillance. Meanwhile, Dax reports that she's found low-level tetryon emissions outside the station. Bashir thinks he can treat O'Brien to nullify the time shifts. Kira says that she's moved the Romulans to new quarters - quarters right next to O'Brien's wall panel.
Later, Odo reports someone's beamed a device into the wall panel. Bashir and O'Brien are hanging out in Quark's bar again. O'Brien gets another trip into the future, and finds himself in the infirmary, looking at his own corpse. He encounters Bashir, who says that he didn't spot the deterioration of his basala arteries until it was too late, and wants O'Brien to tell him in the past to do a scan.
Odo finds a replicator modified into a transporter - his investigation has revealed that the three Klingons on board are a secret strike force spying on the Romulans. Sisko decides they need to arrest the Klingons.
Dax says they're tracking the singularity, which is orbiting DS9 and periodically triggering O'Brien's time shifts. O'Brien timeshifts again, and finds himself on a runabout (piloted by himself) fleeing the destruction of DS9. Other O'Brien doesn't know what caused the destruction because he was asleep in bed at the time the alarm sounded, but says O'Brien must find out what happened when he returns to the past.
Sisko and co are extremely worried and investigate. O'Brien suggests he could try travelling to the future just before the explosion and find out what happened. He and Bashir construct a device and he finds himself 3 and a half hours in the future, where he wakes himself up. Other O'Brien isn't aware of the explosion that destroys the station, and Other O'Brien asks why he doesn't feel as crappy as O'Brien looks. The pair go to ops, where they detect a Romulan warbird decloaking and attacking the station. O'Brien is too far gone to go back and warn everyone, so he hands the device to Other O'Brien, who uses it to jump back into the past and warn Sisko.
Sisko informs the Romulans on the station that he knows about their warbird, and that they plan to collapse the wormhole and kill all the witnesses. The Romulans opt to leave. Other O'Brien admits to Bashir that he's not the original O'Brien, and then goes to bed, but not before teasing Quark briefly.