Kai Opaka, the spiritual leader of the Bajorans, comes aboard the station and requests a tour from Sisko, but during the tour she subtly asks him to take her through the Wormhole. Against his better judgement he complies, and he, Bashir, Kira and Opaka travel to the Gamma Quadrant. There they receive a distress signal from an unknown source. Opaka tells Sisko not to hold back on her account, so the group goes to investigate.

They find a planet with a network of satellites, one of which is malfunctioning. The runabout approaches the planet and one of the satellites attacks it, forcing them to crash land. Opaka dies in the landing, which devastates Kira; however, her mourning is interrupted by a group of people called the Ennis.

The Ennis explain that they are at war with a group called the Nol-Ennis, who could attack at any minute. They take Sisko, Bashir and Kira to a cavelike dwelling and as predicted the Nol-Ennis attack within minutes. Many of the Ennis are killed fending off the attack, but after the battle Kai Opaka enters the cave, regenerated by some form of extraterrestrial nanotechnology. The same technology revives the Ennis and Nol-Ennis, but rather than a blessing it is a curse: Both groups were sent to the planet as punishment for centuries of conflict, doomed to die over and over.

...
Wikipedia