Season 4 of Deep Space Nine marks a major shift for the series, as it introduces a new conflict between the Federation and the Klingon Empire, sparked by the latter's distrust of the shape-shifting Founders. Worf, the former security chief of the USS Enterprise-D, joins the station's crew as Sisko's strategic operations officer, and faces challenges in his loyalty, honor, and family.
Episode 1
Stardate: 49011.4. When the Klingons bring a task force to DS9, Captain Sisko sends for Starfleet's lone Klingon officer, Worf, to uncover the mysterious intentions of their presence.
Episode 2
Stardate: Unknown. Melanie, an aspiring writer, wants to know why Jake Sisko stopped writing at 40. Jake tells how his father died in an accident and then suddenly reappeared.
Episode 3
Stardate: 49066.5. Bashir is asked to help a group of renegade Jem'Hadar break their addiction to ketracel white. Meanwhile Worf is dissatisfied with the way Odo runs security.
Episode 4
Stardate: Unknown. Kira and Gul Dukat go after the lost prison ship Ravinok. Dukat has a secret. Meanwhile Kasidy Yates tries to find work near Bajor, leaving Sisko uncomfortable.
Episode 5
Stardate: 49195.5. Lenara Kahn, the new host of the wife of Dax's former host Torias, comes to the station. While they're not allowed to renew their relation, there's still a spark.
Episode 6
Stardate: 49263.5. A damaged Defiant must play a dangerous game of cat-and-mouse with two Jem'hadar ships inside a gas giant.
Episode 7
Stardate: Unknown. Quark and Rom take Nog to Earth and Starfleet Academy, but a malfunction with the ship takes the crew back in time, to Roswell New Mexico in 1947.
Episode 8
Stardate: Unknown. Worf, Dax and the Klingon Dahar master Kor set out to find an ancient lost relic: the Sword of Kahless.
Episode 9
Stardate: Unknown. When an transporter emergency turns the command crew into holosuite characters, Bashir's James Bond fantasy takes on a deadly reality.
Episode 10
Stardate: 49170.65. Sisko travels to Earth when a bombing at a Federation conference is determined to be the work of Changelings.
Episode 11
Stardate: Unknown. When Starfleet institutes martial law to combat the Changeling Menace, Sisko begins to question if the Dominion is the real threat.
Episode 12
Stardate: Unknown. First Minister Shakaar visits the station, despite a threat of assassination. He falls in love with Kira much to Odo's dismay.
Episode 13
Stardate: Unknown. Dukat returns, stripped of his prestige, to escort Kira to a Cardassian conference about the Dominion. But an attack by a Klingon raider may give Dukat a chance to redeem himself in the eyes of his government.
Episode 14
Stardate: 49556.2. Worf's brother Kurn asks him to perform a death rite to regain his lost honor. Meanwhile Kira and O'Brien investigate Klingon activity near the Bajoran border.
Episode 15
Stardate: Unknown. Unfair working conditions and pay cuts cause Rom to organize a union of the employees of Quark's Bar. Meanwhile Worf still finds it hard to settle on the station.
Episode 16
Stardate: Unknown. A man claiming to be the emissary comes through the wormhole. Sisko is happy to give up his position. Meanwhile Keiko returns and O'Brien stops spending time with Bashir.
Episode 17
Stardate: 49665.3. When Worf destroys a civilian shuttle during an engagement with the Klingons, an extradition hearing is held to see if he must face charges.
Episode 18
Stardate: Unknown. O'Brien tries to re-integrate to life on the station after serving 20 years in a virtual prison.
Episode 19
Stardate: Unknown. When the Mirror Universe counterpart of Sisko's deceased wife lures Jake to the other side, Sisko must follow and help the human resistance against the Alliance's forces.
Episode 20
Stardate: Unknown. A mysterious woman approaches Jake about his future as a writer. Odo promises to do whatever it takes to help Lwaxana Troi keep her baby over the father's wishes - even if it means marrying her himself.
Episode 21
Stardate: Unknown. Sisko must face betrayal when evidence surfaces that Kasidy is smuggling for the Maquis. Meanwhile Garak makes acquaintance with Ziyal.
Episode 22
Stardate: 49904.2. A renegade group of Jem'Hadar plunders Deep Space Nine. Sisko agrees to a combat operation with loyal Jem'Hadar to prevent the renegades completing a planetary gateway.
Episode 23
Stardate: Unknown. Bashir tries to help a planet in the grips of a Dominion-engineered plague that guarantees a painful death.
Episode 24
Stardate: Unknown. Quarks hears on Ferenginar he is going to die. Rom convinces him to sell his remains. After an accident, Bashir has to move Keiko's baby to Kira's womb.
Episode 25
Stardate: 49962.4. Odo is suddenly struck by illness. He is barely able to hold shape. Bashir and Odo see no other alternative then going to the Founders. Garak wants to come along.