The crew encounters a protostar and Captain Janeway decides to have samples beamed aboard for use as a potential power source. A problem occurs when beaming the samples to Voyager.
Janeway recommends to B’Elanna that she should have Ensign Kim's assistance, but it turns out that he is missing. The crew finds his holodeck program Beowulf still running. With each person sent into the holodeck also becoming lost, Captain Janeway sends in The Doctor to investigate, under the assumption that he as an already immaterial hologram cannot be dematerialized the way the missing crew had been. The Doctor shows signs of nervousness when preparing for his first "away" mission, so Kes encourages him to take a name to embolden him with having an identity of his own. He states that he has narrowed his choices to three but does not reveal them.
Once in the holodeck, The Doctor meets Freya, a shieldmaiden, and introduces himself as "Schweitzer". After taking him to the hall, where he is made to prove himself before the others, and after a celebratory meal, after which everyone has retired to separate rooms, she reappears and suggests that, in the cold of the night when the fire in his hearth has gone out, he ought to join her. Though he dismisses her advances, he relaxes his inhibition in later scenes. Later they are confronted by Unferth who kills Freya. She dies in Schweitzer's arms. With her last words she hauntingly speaks his name.
As The Doctor investigates further, he realizes that alien energy lifeforms were beamed onto the ship within the containment field into which the protostar samples were transported. During the transport, one of the lifeforms managed to escape through a breach in the containment field. It escaped to the holodeck and began converting the matter of every person who entered into energy. The Doctor returns the energy samples holding the other lifeforms to the alien in the holodeck; in kind, the missing crew are returned to their original forms.
Afterwards, upon reflection, The Doctor decides not to keep the name Schweitzer, as his memories associated with it are too painful. He remains nameless throughout the rest of the series with notable exceptions in the episodes "Before and After", "Endgame", and "Lifesigns", though other people attempt to give him names.