Opaka is delighted to go through the wormhole, a trip that Sisko notes is the smoothest to date. As they prepare to return, the Yangtzee Kiang picks up a weak subspace signal that the Kai insists on investigating, as she notes that she doesn't get out much. They track the signal to a moon in a nearby system, but the runabout is shot down by the moon's orbital defense systems. The Yangtzee Kiang crashes; although Sisko and Bashir manage to escape injury, and Kira is a little banged up, the Kai is dead. Kira doesn't have much time to mourn, though, as they find themselves surrounded by a group of unfriendly faces.
The leader of the group, Golin Shel-la, takes the crew back to their cave, and identifies his people as the Ennis. He tells them that they are in conflict with a group known as the Nol-Ennis. As it turns out, the planet is a penal colony, where the two groups were banished when authorities on their homeworld couldn't settle their conflict. The Nol pick this time to stage an attack on the Ennis camp, and several members of the two sides are killed before Kira drives off the Nol. Before the Ennis can recover, though, Kai Opaka appears at the mouth of the cave.
Bashir examines the Kai, who appears to be healthy; she doesn't remember dying in the crash, only waking up outside the runabout. While Bashir continues his examination, Sisko and Kira aren't impressed with the lack of defenses that allowed the Nol to stage such a brazen attack. Shel-la reveals the reason why they don't bother, as the fallen rise up as if nothing's happened - nobody on this moon can die, at least not for long, thanks to artificial microbes. When they realized they couldn't die anymore, defensive tactics became pointless. Sisko suggests that Starfleet could rescue the two sides, resettling them separately and allowing them to end the fighting. Bashir, meanwhile, goes back to the runabout to salvage the computers and analyze the microbes.
As O'Brien and Dax begin searching for the Yangtzee Kiang, Sisko convinces Shel-la to have the Ennis and Nol-Ennis call a cease-fire and meet at a neutral site, near the runabout. Kira stays back at the cave with Opaka, who helps the major overcome her guilt for the things she did during the Cardassian occupation. Sisko makes his offer to both sides, but neither side takes him seriously, and the cease-fire is quickly broken. Bashir emerges from the runabout in time to save Sisko from being attacked, and the doctor tells the commander that they can't afford to die on this moon, not even once.
Bashir explains that the biomechanical microbes that revive the Ennis and Nol-Ennis cannot survive in any environment other than that moon, and thus they - and Opaka - are stuck here, as once revived their lives become dependent on the microbes. The Kai reveals that she knew she would not be returning to Bajor, and that she has answered the call of the Prophets - that it is her destiny to try to find a way to bring peace to these people who haven't known anything but fighting for untold ages. She states that she is there to begin their healing process - and that Kira had been there to begin her own.
The Rio Grande finds the planet, and manages to disrupt the satellite defenses enough to allow transport. Bashir suggests that he might be able to disable the microbes to allow the people to die for good, but when Shel-la suggests he would only take the opportunity to wipe out the Nol-Ennis, Bashir drops the idea. Sisko insists that they will find a way to get Opaka off the moon, but she interrupts him, and tells him her work is there now, but that their paghs will cross again. With that, Sisko, Kira, and Bashir beam up.
- Back from the Dead: Kai Opaka, and anyone else who dies on the moon. But only as long as they stay on the moon.
- Death Is Cheap: ...or so one might think. The microbes on the moon that prevent anyone on the moon from dying permanently only work on the moon: if the microbes brought you back, and you try to leave the moon, you will die.
- Dude, Where's My Respect?: Kira is pissed that the official Cardassian file on her describes her as a "minor operative" and errand-girl.
- Forever War: What the Ennis' and Nol-Ennis feud is, thanks to the microbes.
- Inelegant Blubbering: Kira, and why shouldn't she be; her Kai is dead!
- Innocuously Important Episode: Bajor's religious politics have not yet been explored, so the departure of the Kai may not seem like a big deal at this point. But the question of her succession and the ultimate choice for the next Kai will affect future storylines up until the end of the series.
- Plot Armor: Despite all four being sat within a few feet of each other during the crash, the three regular characters escape with few (if any) injuries, whereas the character whose only previous appearance had been back in the pilot episode is so catastrophically injured that she dies within less than a minute of the crash. (Of course she was also considerably older and probably had no experience or training in surviving vehicle crashes like the other three had, but the point still stands.)
- Put on a Bus: Kai Opaka.
- Screw the Rules, I'm Doing What's Right!: Sisko's idea to find a way to transport the Ennis and Nol-Ennis from the prison planet so they can die naturally. When Bashir brings up the Prime Directive, Sisko tells him that whatever their crimes, they've more than paid for them.
- Silly Reason for War: The reason for the Ennis' and Nol-Ennis' conflict is never elaborated upon, but given that one side wears hats, the other doesn't, and there is no other obvious difference between them, the costume designers might have been subtly invoking the trope. Part of the point is that they're so used to war, they've forgotten about any other state of affairs, so it's probably intentional that we never find out - they may not even remember why they're fighting, just that they always have been.
- One leader even says as much, pointing out that there are numerous theories about what might have started the conflict, but that it's irrelevant since it's really the previous actions in the conflict that now what fuel all future actions.
- Techno Babble: Lampshaded:Dax: The magnetic deflection of a runabout's hull is extremely weak. The probes will never be able to detect it.
O'Brien: They will if I outfit them with a differential magnetomer.
Dax: A differential magnetomer?
Dax: I've never heard of a differential magnetomer. How does it work?
O'Brien: I'll let you know as soon as I finish making one.
- The Atoner:
- About a season later we find out that Kai Opaka is in need of some heavy duty atoning for making a Sadistic Choice.
- Kira also qualifies, breaking down in front of Opaka as the horrors of her past in La Résistance catch up with her.Kira: (tearfully) I'm afraid the Prophets won't forgive me.
Opaka: They're just waiting for you to forgive yourself.
- Who Wants to Live Forever?: Not someone who's destined to die and come back over and over again.
- This trope is subverted, however, when Bashir proposes finding a way to turn off the microbes, and Shel-la is only interested in using it to defeat the Nol, rather than allowing his people to be put out of their misery.