When a fatal disease spreads over Bajor, threatening the entireplanet with extinction, Captain Sisko must accept aid from anunexpected source: Ro Laren, Starfleet officer turned Maquisrenegade. Major Kira and Ro reluctantly join forces to track thealien plague to its source -- even as the disease claims newvictims on Deep Space Nine itself. Dr. Bashir strugglesto find a cure, but the secret of the virulent invader may hidedeep in the shadows of Dax's past.