Bashir tries to cure a plague caused by the Dominion.
Bashir, Kira and Dax visit a planet where the Jem'Hadar inflicted the blight, a disease that eventually turns fatal, as punishment for resisting the Dominion. Its people have given up hope, and their healer Trevean only eases them into death.
Bashir stays behind to search for a cure, but his equipment makes the virus mutate. He treats a pregnant woman who dies after giving birth, but her baby is free of the disease, showing that the treatment works as a vaccine. Bashir returns to the station still frustrated that he could not cure those already sick.