When new intelligence claims that the leader of the Klingon Empire is a Changeling, Sisko leads an undercover team -- in Klingon disguise -- to try and expose him.
The crew finds a downed Jem'Hadar warship while surveying a planet in the Gamma Quadrant, and must defend it from the Dominion forces who come to retrieve it.
Quark courts his Klingon ex-wife when she returns to DS9, prompting jealousy from Worf. O'Brien and Kira become aware that their new relationship has uncomfortably romantic implications.
Dr. Bashir and Jake Sisko answer a distress call from a planet near the front lines of the war with the Klingons, where they help a medical facility care for the wounded -- and where Jake learns and important lesson about bravery and cowardice.
Chief O'Brien is stunned when Keiko returns to the station possessed by a non-corporeal entity, demanding that he complete a series of tasks on the station without anyone finding out ... or Keiko will die.
The Defiant is thrown back in time where they encounter James Kirk's Enterprise at a deep space station, and must catch a former Klingon agent bent on killing Kirk and altering the past.
Worf and Jadzia take a vacation to Risa -- with Julian, Lyta, and Quark tagging along -- where they encounter a movement that believes the paradise is making the Federation weak.
Sisko, Odo, Dax, and Gerak fall unconscious after a return from Bajor and find themselves on the station during the Cardassian occupation, appearing as four Bajorans -- forcing Odo to face his past.
Odo transports Quark to testify at a high-security trial, but sabotage forces them to crash-land on a barely hospitable world. Back on the station, Jake and Nog move in together.
Captain Sisko experiences visions that leads to the discovery of an ancient Bajoran city lost for millennia, but which threaten his life on the eve of Bajor's acceptance into the Federation.
Odo comes upon an infant Changeling, and comes to terms with his own past with Dr. Mora when he tries to educate the being himself. Chief O'Brien and Shakaar bicker as Kira goes into labor.
Captain Sisko hunts the traitor Michael Eddington, a former Starfleet officer who has defected to the Maquis terrorist organization -- a mission that quickly becomes very personal.
Gerak and Worf travel to the Gamma Quadrant in search of Cardassian and Federation survivors, and find themselves in a Dominion prison. Dukat tries to evacuate his daughter when he learns that a Dominion fleet is on the way to DS9.
Worf and the others struggle to survive inside a Dominion prison, while Gerak works toward their escape. The station's crew is stunned to learn that the Cardassians have joined the Dominion, with Dukat as the leader of the new government.
A Federation engineer arrives on the station to interview Dr. Bashir's colleagues and family when it is determined that he will be the template for Starfleet's next holographic doctor -- unearthing a secret about Julian's identity.
Odo falls for a mysterious woman with connections to the Orion Syndicate, who is being pursued by a pair of murderous alien criminals who are looking for something.
Quark's accepts his cousin's offer to become a weapons dealer when his accounts hit rock bottom. But he has second thoughts about his new career when a high-profile customer seeks the means to massacre millions of people.
Kira hopes to convince a close friend and leader in the Cardassian dissident movement to spearhead a resistance against Dukat's new Dominion-backed government -- only to learn that he is dying.
Quark returns home only to find that his mother has started a romance with Grand Nagus Zek. Rom and Leeta's relationship is on the rocks when he asks her to embrace some of Ferengi society.
The crew of the Defiant find themselves stranded on a planet in the Gamma Quadrant, where they find a thriving settlement of their own descendents -- caused by the ship going 200 years into the past while trying to escape.
When Captain Sisko learns that the Maquis are poised to launch a devastating missile attack on Cardassia, he enlists the help of the traitorous Michael Eddington to try and stop them.
Chief O'Brien and Garak lead a team to scavenge supplies from Empok Nor, an abandoned Cardassian station similar to DS9 -- but inadvertently revive a pair of assassins left behind to protect the station.
Jake and Nog go to great lengths to try and acquire a twentieth century baseball card to cheer up Captain Sisko. Representatives from the Dominion arrive to negotiate with Kai Winn.
As war with the Dominion grows ever more inevitable, the Federation decides to mine the entrance to the wormhole to prevent more troops from coming through -- sparking a violent backlash.
