The Voyager crew comes across a vast new nebula, and everyone except the Doctor and Seven of Nine are severely affected by its radiation. Since it will take a year to go around it, and a month to go through it, Janeway decides the best course of action will be to put the crew in stasis chambers, which will provide independent life support as they sleep. Seven of Nine and the Doctor will check on their vital signs and take care of the ship until it reaches the other side.
After several days, the lack of social interaction and activity onboard is beginning to put a strain on the Doctor and Seven. Suddenly, the computer alerts them that the anti-matter storage tanks are failing and plasma is leaking. Seven rushes to engineering to eject the tanks, but when she gets there, everything is fine.
The computer is malfunctioning, and false readings were sent to the sensors. While he and Seven are making repairs, the Doctor's program begins degrading. He makes it back to sickbay, but his mobile emitter is no longer working, and he will have to stay there for the remainder of the trip. Now that Seven is even more isolated, she begins having disturbing dreams and visions. When an alien hails her, she beams him aboard and agrees to trade some equipment. His inappropriate comments make Seven feel threatened, and she decides to escort him off the ship. When she turns her head for an instant, he runs away down the corridor.
Although sensors show no evidence of an alien or another ship, Seven searches Voyager for him. She hears voices of the crew calling for her, and the alien begins controlling the ship's functions and playing on her fears. When the Doctor finally gets his mobile emitter to work, he rushes to Seven and discovers that she is hallucinating. The radiation is starting to degrade her Borg implants, and as the EPS conduits overload, the Doctor's program goes off-line. Seven is now truly alone with the fate of the crew entirely in her hands, and she begins to panic.
With 17 hours to go before Voyager clears the nebula, the propulsion system begins to fail. Fighting against more hallucinations, Seven struggles to find a way to reroute power. At every turn she is met by her fears — Borg telling her that she can never survive as an individual, and the crew taunting her about her past deeds in the Collective. With minutes to go, Seven reroutes power from life support to the propulsion system and slips into unconsciousness. When she comes to in sickbay, the crew is awake, Voyager has cleared the nebula, and she has managed to save everyone on board.