5. Phage

An away team is beamed into a network of caverns in a planetoid to search for dilithium deposits. In the course of the search, Neelix is attacked by a previously undetected alien and left in a state of shock. He is beamed directly to the ship's sickbay where it is discovered that his lungs have been transported out of his body. The Emergency Medical Hologram keeps him alive by projecting a pair of holographic lungs into his torso using the sickbay's holographic emitters. As a result, Neelix must remain absolutely motionless, able only to talk, for the rest of his life or until his lungs are recovered.

Another away mission is quickly organized to find the perpetrator and retrieve Neelix's lungs. They return to the planetoid and discover an alien facility behind sophisticated cloaking technology, and conclude that the facility is being used to store organic material, particularly respiratory organs. The aliens escape the planetoid on a ship, and Voyager goes in pursuit. Eventually, Voyager catches up with them and captures the two alien life forms aboard the ship. An interrogation reveals that they are Vidiians, an alien race that have been suffering for generations from an incurable disease called the Phage. The Vidiians harvest organs from other races to replace their own in an attempt to outpace the degeneration caused by the Phage.

It transpires that Neelix's lungs have already been transplanted into one of the aliens, and Captain Kathryn Janeway 's ethical obligations force her to let them go rather than condemn the alien to death by retrieving the lungs. In response to her leniency, the aliens offer to help Neelix, and provide the expertise necessary to perform a transplant from another crew member, a procedure which the Medical Hologram originally considered impossible due to anatomical incompatibility. Neelix receives a donor lung from his partner, Kes.