Preparing for possible invasion by the Jem'Hadar, the soldiers of the Dominion, Kira determines that Deep Space Nine lacks the firepower to defend itself — until Sisko arrives in an experimental vessel called the Defiant, a warship originally designed to fight the Borg. His plan is to travel with his officers into the Gamma Quadrant and locate the "Founders," the unseen leaders of the Dominion, with the purpose of demonstrating the Federation's peaceful intent. If this is impossible, the presence of the Defiant with all of its weaponry will show Sisko's determination to defend against an invasion. Along for the mission is T'Rul, a Romulan with a cloaking device, which will render the Defiant invisible from the Jem'Hadar during the search. Guarding the device is Lt. Commander Eddington of Starfleet Security, who has been ordered to assume Odo's duties. Realizing he is being relieved, an angry Odo resigns.
Meanwhile, Sisko coerces Quark into joining the mission because of his past dealings with the Karemma, a race that lives under Dominion rule. Odo also comes aboard the Defiant at the request of the Bajoran government, but shows to be more edgy than normal. After entering the Gamma Quadrant, T'Rul engages the cloaking device, allowing the Defiant to barely escape detection from two Jem'Hadar ships.
Ornithar, a Karemma official, is brought aboard the Defiant and reveals to Quark and Sisko that a race called the Vorta has ordered all communications for the Dominion directed to a relay station on Callinon VII. Odo's curiosity draws him strangely toward starcharts of the sector, specifically those of the Omarion Nebula. Quark then disembarks while the Defiant heads for the Callinon system. Once there, Dax and O'Brien transport to the unmanned facility. But just as Dax notices that most of the outgoing transmissions are being sent to specific coordinates, her communications to Sisko are cut off. With Jem'Hadar ships on the way, he reluctantly leaves the two behind and orders a course set for the coordinates.
Kira confronts Odo in his quarters to discuss his odd behavior. He confides to her about feeling a mysterious compulsion to travel to the Omarion Nebula — and is convinced that he must go there immediately. Kira tries to make sense of this, but they are interrupted when the Defiant is attacked by three Jem'Hadar vessels.
The Defiant is pummeled by the onslaught, and is boarded by Jem'Hadar soldiers, who overwhelm the bridge crew. Kira and Odo defend themselves, but Kira is shot and falls unconscious. She awakens aboard a shuttlecraft with Odo, who has left the Defiant dead in space. His course — for the Omarion Nebula ...