“The Siege” is episode three of season two of Star Trek: Deep Space Nine.
In the previous episode, “The Circle”, Sisko had obtained proof that The Circle was being supplied with weapons by the Cardassians – something The Circle themselves don’t even know, given that they hate Cardassians. Starfleet had been given a few hours to evacuate all non-Bajorans from the station, and Sisko’s superiors had said they couldn’t intervene in an internal struggle on Bajor, even if it was one supplied by the Cardassians. The Cardassians, of course, want to get Bajor back, and gain control of the wormhole, and the only way they’ll manage that is if Starfleet leaves.
All non-Bajoran non-combatants have been evacuated, but Sisko is staying behind, along with some volunteers. They need to get the information about the Cardassians back to Bajor, but communications have been cut off. Major Kira and Lieutenant Dax have a plan to get there, using a ship that is in less than ideal condition. Getting it through to Bajor is going to be dangerous, and Sisko and the others need to try to capture the Bajorans who are seizing DS9.