Voyager answers a distress call from a Malon freighter loaded with radioactive waste which is about to explode. Chakotay, B'Elanna, two Malon and Neelix board the freighter and try to prevent the explosion and save Voyager.
Early on in the race through the ship to fix its various problems, Chakotay is injured and one of the Malon crew is killed. It is learned that Malon ships are rumoured to be haunted by "the Vihaar" - creatures that sustain themselves by the radiation, and are made out to be rather violent. During a confrontation on the bridge, it is learned that the radiation of the ship tends to mutate crew members, turning them into Vihaar, and it is one of them that seems to be stalking the team. Neelix is badly injured and cannot be beamed out, they must leave the bridge. B'Elanna confronts the mutated crewman. She pleads with him to not attack, but he does and she is forced to kill him. Just in time Neelix and B'Elanna are beamed back to Voyager.
The remaining Malon crewmember is treated and returns to his people.