As Voyager enters a plasma cloud to evade approaching Vidiian ships, Ensign Wildman goes into labor and delivers a baby girl. But as the crew emerges from the cloud, a series of astounding events occur: the warp engines stall, the antimatter supplies drain, and proton bursts cause a hull breach. What's more, Kim is sucked out into space, Kes vanishes in a mysterious void, and Wildman's baby dies.
As the hull breach widens, the ship is forced to run on emergency power. Another proton burst hits and Chakotay orders everyone off the bridge. To her surprise, Janeway sees herself walk across the bridge, which she assumes is a spatial fluctuation caused by their passage through the plasma cloud. Janeway visits Wildman in Sickbay and admires her newborn baby, who appears to be fine. The crew also beams aboard an unconscious patient who's identical to Kes.
This Kes "double" reports the same series of astounding occurrences, which leads Janeway to speculate that there's another Voyager nearby. Apparently, a divergence field has caused all sensor readings to double and every particle on the ship to duplicate. Unfortunately, there isn't enough antimatter to sustain both vessels. Janeway alerts the other Voyager crew, led by a duplicate Janeway. After a merger of the ships fails, Janeway decides to go over to the other ship through the void Kes disappeared into.
The two Janeways meet and strategize their options. The captain of the more heavily damaged Voyager proposes to self-destruct her ship and crew to save the other Voyager. With the Vidiians closing in, the two captains know they must act quickly or both ships and crews will be destroyed. Meanwhile, the Vidiians board one of the Voyagers.
Desperate to steal healthy organs to help battle a plague known as the Phage, the Vidiians begin attacking crewmembers. One of the Janeway captains decides to act. She sets her ship on self-destruct and orders the duplicate Kim to take Wildman's baby through the void. The Vidiians are destroyed when the duplicate Voyager explodes, while Kim, the baby and the other Voyager crew are saved.