While converting the station's old ore processing unit into a deuterium refinery, Chief O'Brien and Jake Sisko accidentally trip an old Cardassian security program, which was set to put the station on lockdown in the event of a Bajoran uprising during the Occupation.

O'Brien, Jake, and Commander Sisko are trapped in the ore processing unit, an area of the station which was once run using Bajoran slave laborers. Fail safes in the system prevent the rest of the crew from accessing the area or beaming the trapped people out. When Jake crawls up the ore chute and tries to break out, the entire station locks down. An image of Gul Dukat plays on all the monitors, announcing that rioting Bajorans have escaped. Poisonous gas is released into the ore processing unit.

In Ops, Major Kira, Dr. Bashir, and Dax have been locked in to prevent presumed homicidal Bajoran workers from storming the station's control center. Odo is dismayed to find himself locked in his security office with Quark.

As the crew works to lift the lockdown program, another fail safe is tripped. The Dukat program on the monitors warns the crew that the whole habitat ring will soon be flooded with poisonous gas. The crew members in Ops are surprised to see Garak wander in. As a Cardassian, his access codes allow him to travel around the station during the lockdown, which was meant only to contain Bajoran workers, not their Cardassian overlords.

He advises the crew to shut off the life support system, which will prevent the release of the poison gas. Unfortunately, this will also leave them only twelve hours to resolve their situation before the oxygen runs out. He discovers he is wrong about that when the Dukat program announces that the station will self-destruct in two hours. When Garak tries to hack into the computer using Gul Dukat's identity, yet another fail safe locks him out and activates an array of weapons in Ops that shoot random blasts of phaser fire. The crew dives for cover.

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