O'Brien nips through the wormhole in a runabout and starts a paranoid flashback log.
O'Brien wakes up at 5:30 in the morning to find Keiko up and acting slightly oddly, taking Molly to school to look at Vulcan learning programs. Then he finds an engineer working on the security grid, which he thought was waiting for Odo to come back, and spots Keiko chatting with Sisko.
Outside the flashback, O'Brien is heading for the Paradas system. The computer detects another runabout in pursuit, but he continues his flashback.
Bashir want to give O'Brien his physical and though O'Brien isn't keen, Sisko insists. Then asks for advice on an oncoming visit by the Parada. Also, he says he was chatting with Keiko because Jake's grades are down. O'Brien goes for his physical, which takes far too long, but ends with Bashir giving him a clean bill of health.
Jake asks O'Brien about help with a subspace transceiver, and says his grades are great. O'Brien goes to check out the upper pylons, and, realising it's going to keep him busy a while, goes to check out the security arrangements for the Paradas. Apparently he can't get in to check them, because only Kira has the access codes, and Sisko wants O'Brien working on the upper pylons. O'Brien spies the engineer entering the restricted area shortly afterwards.
Jake shows O'Brien a component he's replicated, but is called away by Kira when O'Brien asks about what's been happening while he was off-station. Keiko's still acting oddly, not having sex with him and making him his favourite food (ooo, SUSPICIOUS!). He makes an excuse and doesn't eat any, because it's clearly poisoned. O'Brien is now convinced this isn't the real Keiko.
Hmm, this seems like a somewhat more subtle version of The Voyager Conspiracy...
O'Brien scans the station and finds nothing wrong, then finds he's locked out of the station logs made since after he returned from the Paradas system. He breaks into the computer logs and finds that everyone's been snooping in his personal logs and scrutinizing his reports.
Odo returns to the station and O'Brien intercepts him at the airlock to tell him about how everyone's acting oddly. Odo says he'll do some investigating. O'Brien goes to Quark's bar and engages in conversation with the Ferengi, who doesn't seem to be in on the conspiracy. Finally, Odo says he's come up with something. Unfortunately Odo now seems to be in on it too - Sisko, Kira and Bashir turn up to ambush O'Brien, and he makes an escape.
Run, O'Brien, run!
They try to trap him with force fields, so he activates every force field on the station, forcing them to shut down the force field system. Then he runs into Jake, who tells him to surrender. With everyone hunting for him, O'Brien ducks into the maintenance shafts and reaches a cargo bay, where he's able to use a transporter to get aboard a runabout and escapes under phaser fire. He contacts another Starbase to warn them about the conspiracy, only to find the Admiral is in on it too. He nips through the wormhole and heads for the Paradas system, which takes us up to where he's making the log.
He manages to evade the pursuing runabout using the magnetic pole of a moon, and then follows it to Parada 2, where he beams down and interrupts Sisko and Kira talking to the Paradan rebels. One of the rebels shoots him, but a door opens to reveal... another O'Brien. The first O'Brien is a replicant designed to assassinate someone. Fake O'Brien dies. Teh end.
Nice plot twist!