As Voyager helps a generational ship of Varro repair their warp drive, Kim and a female Varro, Tal, become attracted to each other. Knowing that Kim is violating several rules of protocol, they sneak away to Tal's quarters to be together. While they are making love, light flickers just below the surface of their skin. Later, the luminescence returns to Kim's skin, and Seven of Nine insists he go to sickbay.
When the Doctor thinks he has contracted a virus, Kim confesses to his intimate relations. Janeway is notified, and she orders him to stop seeing Tal. The Captain believes that Kim has put the crew's relationship with the Varro at risk. After Kim tells Tal the luminescence returned, she explains it is what they call olan'vora, or the shared heart. The more time they spend together, the harder it will be to part. He tries to leave, but they kiss instead. Meanwhile, Tuvok and Neelix discover a Varro male hiding in one of the Jefferies tubes. When questioned, he reveals he is seeking asylum on Voyager. He says many Varro feel imprisoned on their ship and there are rumors of a violent movement to leave it.
After finding microfractures in Voyager's hull, Seven and Torres discover silicone-based parasites are present. They are synthetic and believed to be an act of sabotage. First planted on the Varro ship, now the parasites have migrated to Voyager. On the shuttle, Kim and Tal secretly rendezvous and fly to a nearby nebula. When Tuvok tracks them down, he informs them both to report to Voyager.
A schematic for the parasite was found on Tal's personal database, and she reveals the dissident group is dismantling the Varro ship. The parasites are targeting the linkage between segments, which will break off into separate ships and allow people to choose whether to stay or go. When Janeway explains the decay will cause decompressive explosions, Tal agrees to slow down the parasites long enough for the ship to be evacuated. Janeway orders Kim to sickbay to treat the bio-chemical bond he has developed with Tal, but he refuses. As they argue, the Varro ship experiences structural breaches, and Voyager is unable to separate from it.
With only minutes before collapse, Janeway agrees to Kim's suggestion to extend Voyager's integrity field around the Varro ship and buy them more time for evacuation. Once completed, Voyager detaches, and the Varro vessel breaks off into several separate ships. Their leader, Jippeq, is forced to let the dissidents seek out their own path. After he and Tal say good-bye, Kim refuses to take medicine for his lovesick condition, preferring to let the pain remind him of the happiness he felt.