Miles "Smiley" O'Brien struggles to hold together his fragile band of rebels in the fight against the overwhelming forces of the Klingon-Cardassian Alliance. The standoff provokes increasingly frequent and violent clashes of wills between Regent Martok of the Klingon Empire and Legate Dukat, leader of the Cardassian Union. Dukat plans a secret invasion of Terok Nor as a means of gaining the political upper hand within the Alliance. Light-years away, Mac Calhoun and his Romulan allies harass Klingon forces with hit-and-run attacks. It's an ultimately futile strategy, but Calhoun doesn't know what other options he has. So he fights on...

Behind the scenes, Memory Omega-the secret operation initiated by Spock more than a century earlier-is coming to fruition sooner than planned. But moving early involves risks, and if the leaders aren't careful, all of Spock's work will be for nothing.