The attackers contaminated the inhabitants with a terminal disease that is passed on from generation to generation. The Blight, as the malady is known, causes blue lesions all over the faces of sufferers. When the afflicted near death — a period called "the quickening" — the welts become red and inflamed while the disease grows very painful. Bashir and Dax transport to the planet's surface, where they encounter a woman and take her to a hospital. But they soon discover that Trevean, the hospital's "healer," is in reality a man who poisons those who are quickening in order to end their suffering. Bashir wants to help save them, but Trevean insists that there is no cure.
However, a woman named Ekoria privately seeks Bashir's help — she is pregnant, and afraid she will not live to have her baby. Bashir and Dax decide to stay and try to find a cure, while Kira leaves in the runabout so the Jem'Hadar — hopefully — won't detect their presence. Bashir then begins studying the disease. With Ekoria as a volunteer, he isolates the virus, but since she is in the dormant phase, he cannot complete his research. However, few people in the quickening stage are willing to help him — even if it means they could be saved. Bashir fixes a boy's broken arm to prove that his healing powers are advanced. However, Trevean tells him that his people have been fooled before, and that no one has yet found a cure. Finally, Epran, a man in the quickening stage, volunteers, and a few days later, Bashir has a makeshift infirmary full of patients, all in a similar condition.
He injects everyone with doses of what he believes may be a cure. After a little while, however, Epran suddenly gets dramatically worse. Bashir discovers the virus is mutating. Realizing the electromagnetic fields from his medical instruments are responsible, he frantically shuts down everything, but it's too late — all the patients die horrible, painful deaths. Trevean shows up to put the sufferers out of their misery, while Bashir reflects on his failure. Later, he runs into Ekoria, who has entered the quickening phase. Realizing she will probably die before her child is born, Bashir gains new resolve, then chooses to stay on the planet while Kira and Dax return to the Alpha Quadrant.
After drawing Ekoria's blood, Bashir is disappointed to discover that her body has not one trace of the antigen he had given her. Knowing Ekoria will not survive to see her baby born naturally, Bashir decides to induce labor in two weeks. Ekoria's suffering worsens, and Trevean eventually goes to see her, offering to help her and the unborn child die. But Ekoria chooses to give her baby a chance to live, and Trevean wishes her well. Finally, the child is born, and Ekoria lives just long enough to see a miracle. While the antigen did not work on her, her baby is born without lesions — meaning he doesn't have the Blight, and that the fetuses of pregnant women can be vaccinated against it. While Ekoria's generation will die, their children will survive, and her people's suffering will finally end.