Chief Engineer B'Elanna Torres dismisses the VulcanEnsign Vorik at the end of his shift in Engineering. Before Vorik leaves, he turns to her and declares kunat so'lik - the ritual Vulcan marriage proposal. Specifically, Vorik intends that B'Elanna will become his mate. He explains that he has an intended bride back at home, but since Voyager is not likely to reach home anytime soon, he has decided to pick a mate aboard the ship, and has found B'Elanna suitable. Flabbergasted, she declines. He grabs her, cradling her face, and she punches him.
As he mends Vorik's dislocated jaw in Sickbay, The Doctor discovers that the ensign is beginning his first pon farr. He is in a sexual frenzy and requires a mate. Since there is no mate available, Vorik decides to meditate. The Doctor summons Tuvok to advise the younger Vulcan, though Tuvok is extremely reluctant to do so at first.
Meanwhile, B'Elanna joins Tom Paris and Neelix for an away team mission to a planet to lay in a supply of gallicite from an abandoned mine. She becomes increasingly aggressive and agitated, snapping at Neelix and refusing to cooperate with her teammates. She attacks Paris, biting him savagely on the cheek and then stalking off on her own. When Paris reports back to Voyager, his description of her behavior leads Tuvok to conclude that she has contracted pon farr from Vorik, since the ensign had initiated the telepathic mating bond when he seized her face in Engineering.
Tuvok and Chakotay travel to the planet's surface and descend into the mine to help Paris hunt down the addled B'Elanna Torres. They tell her that her discomfort is from the pon farr, and she needs to return with them to the ship. The transporter will not reach so far underground, so she must return to the surface. Before they can persuade her, the away team is surrounded by aliens called the Sakari; the mine is not abandoned after all. The aliens disappear and take Tuvok and Chakotay with them. Now alone with Paris in the mine, B'Elanna tries to seduce him. She is in heat and, having already chosen Paris as her mate with the bite on the cheek, is determined to have sex with him. He admits that he would like to oblige her, but refuses to take advantage of her while she is in such a state.
Tuvok and Chakotay discover that the aliens are peaceful, just a little jumpy after having run from previous invaders on their planet. Back on the surface, Tuvok advises Paris to have sex with B'Elanna to help purge the pon farr. He awkwardly agrees, but before the two can engage in the act, Vorik storms in to claim B'Elanna, challenging Paris to the kunat kalifee, a ritual fight. B'Elanna angrily rejects the idea, declaring that she'll fight Vorik herself. Both fight aggressively, though B'Elanna defeats him, and both are purged of their pon farr. Afterwards, she and Paris admit to each other that they might have a future together.
As the away team prepares to leave the planet, they make a horrifying discovery. The invaders the Sakari were running from were Borg.