A planned power outage causes the Borg children to wake from their regeneration cycles, much to their surprise. Neelix is there to comfort them. The children wonder if this incident has anything to do with a highly restricted area on Deck 12. After all Naomi Wildman has told them, Mezoti thinks a ghost is present there. Voyager is shown drifting into a nebula.

Neelix proceeds to distract them with a story they only partially believe, concerning an entity that was accidentally taken in by Voyager. This story allegedly takes place a short period before the Borg children had come aboard the ship, so they do not know if it is true.

After Voyager leaves the nebula, they experience many system's malfunctions, first annoyances then more serious. Navigation and communications become completely off-line, and life support—although not gone—is erratic. Through various circumstances, apparently thrown in by Neelix to add tension to the story, several suspenseful situations arise: Ensign Kim and a female crewman become the only two on several abandoned decks, Tom Paris is brutally injured by an electric discharge from his console, the Doctor goes offline, and Tuvok and Neelix must get to safety by themselves. On their way to Engineering, Tuvok is injured by an electric discharge similar to the one that struck Lt. Paris.

In Engineering, Janeway plays a hunch and talks to what was previously assumed to be a communication malfunction, but is in fact the entity trying to speak. Eventually, Janeway is able to talk to the entity, and realizes that the malfunctioning systems have been its attempt to return to the nebula where it lived.

Relieved, Captain Janeway takes the ship back to the coordinates of the nebula—only to find it has disappeared. Apparently, Voyager's passage through the nebula had destabilized it. The entity, still aboard Voyager, becomes very angry, and begins depleting oxygen from all decks. Repeating frequently "Abandon ship", it intends to make Voyager its new home.

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Wikipedia