Arriving at their first assignment to find the seventh fleet decimated, the crew of the USS Argus set out to rescue the survivors before the Dominion fleet returns. Meanwhile one of those survivors has made a discovery on the surface of a nearby Dominion occupied planet that could change the course of the war.

Kate Sheridan comes face to face with her past when she and several other Argus crew members are sent to recapture a hijacked Federation starship. Meanwhile Sara Parker discovers a hidden signal that could have huge repercussions for the Argus and her crew.

Trapped in Earth's past, Captain Lex and the surviving crew of the USS Defender must try to survive a nuclear holocaust that will kill millions while ensuring history runs its course. Back in the 24th Century, Commander Patel and the crew of the USS Argus investigate a three hundred year old ship that appears to be the source of a mysterious signal.