The "genatron", eh? Sounds mildly dodgy. That pre-credits teaser is... extremely vague.
Apparently Paris, Torres and Red Shirt are offship on a mission. On Voyager, Neelix is attempting native Vulcan dishes. He decided to spice up the soup, for some reason. Well, because he's a dick, basically.
They arrive at the planet where the away team is off on their mission, and find that the cave system has changed. Chaks takes a team down to search for them.
Torres, meanwhile, is captive of a Vidiian doctor, Sulan, and appears to now be full-Klingon. Science doesn't work that way. She presumably only has half the genetic material of a Klingon. Sulan says Klingons are immune to the Phage, and he's infected her to try to work out why.
Meanwhile, Paris and Lt Red Shirt sit in the cells and discuss trying to escape, to the amusement of a Talaxian prisoner, who says Torres has probably been taken to get her organs recycled.
Klingon Torres suffers Phage symptoms, and Sulan is impressed by how well she stands up to it. Sulan wants to try to integrate her genetic code into the Vidiian genetic code so he can cure the Phage.
Meanwhile, Paris and Red Shirt are joined in their cell by a fully-human and somewhat bewildered Torres, who proceeds to angst at length about her childhood.
Chakotay's team, who have been wandering around aimlessly, find that the tunnel system has changed, and Tuvok says it's a Vidiian force field. After unsuccessfully trying to break through it, they spot some Vidiians and cowardly beam up.
KlingonTorres unsuccessfully gives Sulan the come on to try to get him to let her go. As he points out, he's quite ugly, and then kills Lt Red Shirt and has his face grafted onto his own. Enraged, KlingonTorres breaks her bonds and attacks him.
I like to think that after the Phage was cured, the Vidiians devoted themselves to being full-time doctors and travelled around helping other races as a way to make up for being dicks. But... Voyager never really explored that aspect of it.
HumanTorres doesn't do so well in the mines, and admits she was terrified when the Vidiians took Lt Red Shirt. Paris attempts to pep talk her, but she ends up being taken back to the barracks.
The search for the away team continues! Chakotay's been disguised as a Vidiian and beams down to look for the away team. Their's is a stupid plan.
KlingonTorres rescues HumanTorres, who immediately faints and has to be carried by her other self. Later on, by the camp fire, KlingonTorres wakes her other half and offers her fried rat. Then they argue over which of them is crap. HumanTorres has a plan to shut down the force field cloaking the Vidiian base so Voyager can beam them out. They break back in, and HumanTorres sets about deactivating the force field. Sulan gets the drop on them, but then Chaks and PAris turn up to give them a hand. Sulan tries to shoot HumanTorres, but KlingonTorres jumps in the way and is mortally wounded because they beam up.
KlingonTorres dies, but HoloDoc is able to work out a way to reintegrate the Klingon DNA into HumanTorres using the little known "Reset Button Procedure" so she can be half-Klingon again.