DS9 Season 7 Episode 17 Penumbra

Plot

Worf is reported lost in a perilous region of space known as the Badlands after the ship he was commanding was destroyed by a Dominion attack; the USS Defiant recovers some survivors of Worf's ship but not Worf himself. Ezri Dax, feeling an obligation to Worf due to her memories of Jadzia, takes a runabout to the Badlands to search for him herself. Dax has the computer extrapolate a likely entry point for Worf's escape pod into the Badlands, and then takes the runabout in and cuts the engine, allowing the currents to carry her to Worf's position.
Once Dax has rescued Worf, their conversation on the runabout is awkward; he resents her treating him as if she were Jadzia. When the runabout is attacked by Dominion ships, they escape by transporting themselves to a nearby planet, but have no way of calling for help. Camping on the planet for days, they argue about Jadzia; their fight eventually turns into a kiss and then sex. Later that evening, the two are abducted and imprisoned on a Breen ship.
Meanwhile, side plots in the episode focus on other character arcs and subplots in the Dominion War story arc:
Sisko buys land on Bajor, planning to build a house there for his retirement, and proposes marriage to his girlfriend Kasidy Yates. However, he receives a vision from the Prophets, who tell him that marrying Yates will bring him great sorrow. The Changelings are secretly suffering from an unexplained illness, and no progress has been made in finding a cure. The Cardassian leader Damar is growing more and more discontent with Dominion rule. He is visited by Dukat, his predecessor as leader of Cardassia, who has become a member of a cult worshipping the Prophets' enemies, the Pah-wraiths; Dukat undergoes cosmetic surgery to disguise himself as a Bajoran.