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.
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.
Stardate: 49011.4. Sisko becomes uncomfortable when the Klingons station a task force to help defend against the Dominion. Worf is summoned to find out their true intentions.
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.
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.
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.
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.
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.
Stardate: Unknown. When an transporter emergency turns the command crew into holosuite characters, Bashir's James Bond fantasy takes on a deadly reality.
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.
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.
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.
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.
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.
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.
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.
Stardate: Unknown. Sisko must face betrayal when evidence surfaces that Kasidy is smuggling for the Maquis. Meanwhile Garak makes acquaintance with Ziyal.
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.
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.
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.