A reluctant Commander Benjamin Sisko arrives at Deep Space Nine, a former Cardassian space station, and discovers that it borders a unique stable wormhole leading to the Gamma Quadrant.

The Cardassians declare war, damaging the space station during the battle, but hostilities cease when Sisko returns with the missing Cardassian ship.

A member of the Bajoran underground seeks asylum on DS9, attracting the attention of Cardassians and Klingons, and testing Kira's loyalties.

Mounting evidence points to Security Chief Odo as the murderer of a Bajoran criminal under investigation, and Keiko tries to establish a school.

A virus that causes its victims to speak in gibberish breaks out on DS9, and Sisko assigns Kira the job of finding an antidote.

Through a new friendship with a bizarre alien, O'Brien and the rest of the officers of DS9 learn that other beings do not respect life as much as they do.