Prophecies about the Bajoran wormhole come due with a Cardassian visit.
Cardassian scientists come to help set up a communications relay through the wormhole, and Vedek Yarka warns Sisko of a prophecy that three vipers will bring destruction to the Celestial Temple. Kira, increasingly troubled, struggles between her faith and her duty to Sisko, whom many Bajorans see as the Emissary.
One of the three scientists turns out to be an Obsidian Order agent sent to sabotage the project. A comet's silithium fragments threaten the wormhole, and Sisko and Kira steer them through. The reaction that follows creates the very link the project needed, and the prophecy appears to be fulfilled in a hopeful way.