When the ship encounters a swarm of space-dwelling lifeforms, the crew first opts to study them from a distance. But after the creatures draw Voyager into their midst, their unusual energy patterns create problems for many of the ship's systems and cause some very strange symptoms in Kes. First the Ocampan begins eating everything in sight. Later she becomes delirious, and her body goes through peculiar changes.

As the crew tries to figure out a way to move away from the lifeforms without harming them, the Doctor examines Kes and discovers that they are wreaking havoc with her metabolism. They are pushing her prematurely into the "elogium" — the phase in which Ocampan women become fertile. The process occurs only once in an Ocampan's life, so if Kes ever wants to have a child, she must do so immediately.

Janeway and Chakotay discuss the implications of having babies on board Voyager, while Kes asks Neelix to father her child. Neelix's initial hesitation causes Kes to question whether he really wants a baby. Later, Neelix consults with Tuvok about the pros and cons of parenthood. Finally, he returns to Kes and tells her he's ready, only to discover that now she is having second thoughts.

Anxious to escape the swarm, the crew attempts to move away, but the swarm follows. Suddenly, an even larger version of the creatures appears and blocks Voyager's way. Bewildered at first, the crew realizes that it is a "suitor" for the swarm and that it thinks Voyager is a rival. Every aggressive move they make is met by a stronger countermove from the creature.

Finally, Chakotay suggests the ship act submissively by "rolling over." Happily, the plan works and the swarm moves away with the big creature. Later, Kes ultimately decides against having a baby, but is relieved by the Doctor's belief that her elogium may have been a false alarm brought on by the electrophoretic field created by the swarm; it could recur later. Ironically, Janeway learns that an ensign named Wildman is pregnant, so the crew will soon welcome a new arrival after all.