On an astronomical black hole observation mission, SG-1 finds a fatal bacterial mass-epidemic on a planet where the natives told then-incredulous Daniel months ago that the coming solar eclipse would bring disaster. They also take back to the Cheyenne Mountain Base a surviving, fairly healthy, orphaned young girl named Cassandra, and awakes Sam's maternal instinct. The Naquadah traces found in her blood turn out to have made her immune, but after she has a seizure they are diagnosed to constitute a huge bomb, somehow triggered by rescuing her; the whole thing must be planned as a 'Trojan Horse' by the Goa'uld. Sam takes the prospect of sacrificing Cassie personally and is prepared to take personal risks.