A Cardassian colony in the Demilitarized Zone that is contaminated by the Maquis with cobalt diselenide in For the Uniform, forcing its population to flee.
Quatal Prime is one of two Cardassian colonies struck by Michael Eddington's Maquis cell in For the Uniform, the other being Veloz Prime. Maquis raiders seed its atmosphere with a biogenic agent that will make the planet deadly to Cardassians for years to come while leaving other species unharmed.
The Defiant, crippled earlier by a computer virus that Eddington left behind when he defected, reaches the area too late to prevent the attack. Eddington then draws Sisko away by damaging a Cardassian evacuation transport, obliging the Defiant to break off and rescue the passengers.
The attacks push Sisko into his most ruthless act of the series, the poisoning of Solosos III. Eddington surrenders to stop him from doing the same to other Maquis worlds, and the refugees of Quatal Prime are expected to move to the colonies the Maquis have had to abandon.