At the end of Act Four, we’d just seen Sisko, Kira, Quark, and others, trick the Cardassians into leaving a game they were playing in Quark’s Bar, and transferring their winnings into a “bag” which later turned out to be a shapeshifted Odo. By transferring back to the Cardassian ship, Odo was able to sabotage their ship to prevent them from following Sisko and Dax, who had just left for the Denorios belt in a runabout to in order to locate the other Bajorian Orbs, one of which had been gifted to Sisko by Kai Opaka, Bajor’s spiritual leader, as she believed that it was his destiny to find the origin of the obs, Celestial Temple of the Prophets.
The coast is now clear for Sisko and Dax to embark toward the Denorios belt, the coordinates of the focal point of the Bajoran Orbs. As Dax steers the vessel toward high proton counts and the external wave intensifies, while internal wave intensifies remains unaffected, a wormhole suddenly opens directly in front of them. They are pulled into it, as DS9 loses contact with them, picking up only major subspace disruptions. The Rio Grande emerges in the Gamma Quadrant, some 70,000 light years from its previous location. Sisko suspects that the wormhole is the source of the Bajoran Orbs, and realizes that they have discovered the first stable wormhole known to exist, so they turn around and attempt to return to the Alpha Quadrant.
However, the Rio Grande loses power and velocity while in the wormhole; they land on a “planet” with breathable atmosphere. To Sisko, it appears to be a barren wasteland, raging with electrical storms; to Dax, however, the planet appears beautiful, like an idyllic garden setting.
A hovering Orb appears and scans their bodies; it engulfs Dax and takes her through the wormhole safely, and she materializes in Ops on DS9. Sisko is transported from the imaginary planet to the Celestial Temple, where he begins another vision, this one being his first communication with the Prophets of the Celestial Temple.
The Prophets are non-corporeal entities, appearing to Sisko as people in his life: his late wife Jennifer, Picard, the kai, and Jake. They seek contact with other lifeforms, but do not consider him worthy, since he is corporeal, and relies on crude linguistics for communication. As he tries to defend himself and his species, Sisko seeks to develop some form of communication protocols with them.
“First officer’s log, stardate 46392.7. We’re preparing to launch a rescue mission to find Commander Sisko, but first, our navigational sensors must be recalibrated to work under the conditions reported by Lieutenant Dax.“
Once Kira realizes what Sisko and Dax discovered, she recognizes its tremendous importance and orders the entire DS9 space station to be moved to the mouth of the newly-found wormhole. With only six functional maneuvering thrusters, O’Brien states that it would take two months to cross the 116 million kilometers to the wormhole. Kira replies that it has to be done by the next day, stating that the Bajorans have to stake a claim to the wormhole, then in an apparent change of attitude, notes that the Federation’s presence would strengthen the claim. Dax suggests they lower the inertial mass of the station with the deflector array; O’Brien begins work on this endeavor. Dax contacts Starfleet for assistance; the nearest starship is the Enterprise, which is two days away. Kira, Dax, and Doctor Bashir decide to set out toward the wormhole in another runabout, the USS Yangtzee Kiang, to rescue Sisko. Odo insists on joining their expedition, citing his own discovery in the Denorios belt and how his origins may be related to the wormhole phenomenon.
Back inside the wormhole, Sisko communicates with some non-corporeal aliens who take the form of several people he knows; Jake, Picard, Locutus of Borg, Kai Opaka, Jennifer, and the crew of the Saratoga, among others. The aliens discuss destroying the intruder, while Sisko insists he was sent by the Bajorans. In order to prove he means no harm he offers to allow the aliens to share in his experiences and his past. However, it turns out the wormhole aliens have no concept of linear time. They refuse the idea that the past, present, and future are in any way different from one another.
As Sisko and the wormhole aliens try to understand one another, O’Brien and the crew attempt to find a way to safely move DS9 to the mouth of the wormhole, but the Cardassian computer is less than cooperative to the point where it refuses to cooperate with some of his requests. With great difficulty, O’Brien manages to move DS9; however, Dukat has become aware of the wormhole’s presence.
Suspecting Sisko of already striking a deal with “whomever” in the wormhole, Gul Dukat races toward the wormhole himself; his Cardassian vessel, easily out-pacing Kira and the runabout, proceeds through the wormhole.
Meanwhile, Sisko is showing the aliens a moment in his past when he and Jennifer were sharing a picnic. The aliens mention that Jennifer is a part of Sisko’s existence, but Sisko tells them that while she was a very important part she is not anymore as she is no longer alive… he lost her. The aliens are now very confused, unable to understand what “lost” means. Sisko tells them that when in linear time, people are unable to go back to the past, when something is lost it is gone forever. The aliens cannot understand how any species could possibly survive in this manner.
Sisko goes on to explain that this day is important as it affected every one that followed; it is the day he and Jennifer decided to have a child. As the two echoes kiss, Sisko starts to explain about touch and pleasure when suddenly…
…he finds himself back on the Saratoga, standing over his wife’s body. The aliens explain this is his existence. Sisko tells them that this memory is more difficult than any of the others because this is the day he lost Jennifer. The aliens don’t accept this, and they ask Sisko why he exists here. Sisko doesn’t understand what they’re asking, but they insist that he exists here.
Suddenly, everything stops. Gul Dukat’s ship is traveling through the wormhole and emerges in the Gamma Quadrant. In anger, the aliens seal the wormhole, preventing the Yangtzee Kiang from following.
The aliens explain to Sisko that whenever someone travels through the wormhole their existence is disrupted, therefore they have closed it. The aliens tell Sisko that his linear nature makes him naturally destructive and he doesn’t understand the consequences of his actions, a charge Sisko denies. He tells them he is aware that every choice he makes will have a consequence, even if he doesn’t know what it is. To help, he uses past experiences to guide him. For example, he cites the day he met Jennifer on the beach and how their past experiences helped them realize they had a future together and when they got married they accepted any of the consequences that would come from that act… including the birth of their son.
The aliens are starting to understand but still need help, so Sisko decides to use the game of baseball as an example. He tells the aliens that when he throws the baseball anything could happen, the batter could swing and miss or he might hit the ball perfectly. A person prepares for every consequence as they happen, and as a result the game will start to take shape even though no one knows what the outcome will be. Now the aliens start to get it, but now can’t understand why Sisko values his ignorance of the future. Sisko tells the aliens that the unknown is what drives his species, that they are always exploring and looking to the future to expand the boundaries of their knowledge. He explains that he isn’t there to conquer them, but to co-exist and share their knowledge.
“If all of this is true, why do you exist here?!“
Sisko is once again on the Saratoga looking at his wife’s body under the debris, confused why the aliens keep returning him to this point.
“First officer’s log, supplemental. We’ve rendezvoused with the space station at the former coordinates of the wormhole. Unfortunately, our scans have revealed no trace of either the wormhole or Dukat’s ship. A few minutes ago three Cardassian warships crossed the border, no doubt on their way to search for Dukat.“
In light of Dukat’s disappearance, the station is soon approached by three Cardassian warships, which take a threatening posture. Gul Jasad demands to know the location of Dukat’s vessel; he refuses to believe Kira’s “wormhole” explanation, since there is no sensory evidence of such. Jasad allows Kira one hour to prepare for surrender, but with the Enterprise still twenty hours away, Kira knows that surrender is not a viable option.
Inside the wormhole, Sisko demands to know why the aliens keep bringing him back here to the Saratoga but the aliens tell him they are not bringing him here, he is taking them there. Sisko asks for the power to take them somewhere else, but the aliens tell him that he already has the power but is denying himself it and should look inside himself for the answer. Sisko then looks back, and sees himself from three years earlier, desperate to free his wife despite the knowledge she was dead. Sisko notes that he was ready to die with her.
Sisko is clearly in pain at recalling the most horrific of his memories, and the aliens sense this and try to comfort him. As he sees his past self dragged away he realizes inside that he never completely left the Saratoga. As he looks down at his wife, and through his tears, he tells the aliens that the moment he looked down at Jennifer’s dead body has always been in his mind, he sees the same image when he is in the darkness or when he closes his eyes. The aliens realize that none of Sisko’s past experiences helped prepare him for this consequence and Sisko confesses he’s never been able to get over losing her and that inside he does still exist here. But finally Sisko realizes that Jennifer is really gone and he has to let her go forever. He grieves properly this time, letting go of his emotions, but finally starts to leave the trauma of his wife’s death behind him.
Kira launches six photon torpedoes – the station’s entire complement – as a bluff, to make Gul Jasad believe that Starfleet has replenished DS9’s weaponry after taking over the station. The bluff fails, however, as the Cardassians begin assaulting the station, easily penetrating its weak shields and causing an explosion on the Promenade which leaves many people injured. Odo calls for medical assistance from Doctor Bashir who immediately leaves Ops to tend to the wounded.
Dax reports that their shields are down to eighteen percent and rapidly falling. Kira, knowing another assault would likely destroy the station, is about to surrender when Dax suddenly reports a huge neutrino disturbance 15 kilometers off the docking ring; the wormhole is back.
The wormhole opens in an explosion of brilliant, neon-like light; the Cardassians, shocked to see it for the first time, immediately cease firing on DS9. To everyone’s surprise, Commander Sisko emerges in the Rio Grande, towing Gul Dukat’s disabled vessel from the wormhole to safety. Once securely back in the Alpha Quadrant, Dukat orders the Cardassian vessels to stand down.
Luckily there were no fatalities on DS9, just various injuries being treated by Doctor Bashir and Odo, who has been pressed into medical duties, for the time being. Sisko, back aboard DS9, joyously greets Jake. The aliens living in the wormhole, whom the Bajorans believe to be the Prophets, have granted Sisko and all other corporeal beings free passage through the wormhole. And with the return of the Enterprise, the Cardassian vessels retreat back to Cardassian space.
“Station Log, Commander Benjamin Sisko, Stardate 46393.1. The lifeforms who created the wormhole have agreed to allow safe passage for all ships traveling to the Gamma Quadrant. With the arrival of the Enterprise the Cardassians have left the area.“
Meeting once again with Captain Picard, this time in Commander Sisko’s office, he is congratulated on finding the wormhole; Bajor will now undoubtedly become a commercial and scientific hub, as well as a strategic military focal point for the Federation. Sisko retracts his earlier conversation with Picard, about possibly resigning his commission. Picard, who had not forwarded the information up the chain of command, nevertheless asks Sisko if he is sure about staying at the helm of DS9. Sisko assures him that he is; Picard shakes his hand, and leaves for the Enterprise, wishing Sisko good luck.
Kira warns Quark to not cheat his customers anymore, but allows him to keep his bar open. As the repairs continue, Dax and O’Brien inform Sisko about the impending arrival of three Frunalian science vessels and a related problem with the airlocks, as the station and its crew begin their new roles in galactic affairs.