When the U.S.S. Voyager picks up a distress call, Janeway finds escape pods contaminated with radiation. Two survivors, Fesek and Pelk, are beamed to sickbay as the crew discovers the source of the radiation is a disabled Malon freighter. During a mission to export their toxic waste, a leak forced them to evacuate. Fesek explains that when the ship explodes, the waste will ignite and destroy everything within three light-years. Before Voyager can travel to a safe distance, its warp drive collapses. Now, the crew must board the Malon ship and disable it.

With only six hours to go before the storage tanks explode, Fesek, Pelk, Chakotay, Torres and Neelix beam to the freighter. They plan to start in the least affected chamber and clear a path to the control room by opening airlocks and decompressing the ship. An inoculation created by the Doctor affords them a few hours of protection from the radiation. While checking on a jammed airlock, Pelk is attacked by a creature superstitiously believed to be created by radiogenic waste.

Pelk tries to convince the team that the creature exists, but they think he is hallucinating. When he dies, Pelk is beamed to sickbay to determine his cause of death. Meanwhile, Janeway prepares a contingency plan based on a nearby star. She concludes the corona would absorb the radiation from the blast if the freighter could be nudged close enough to it. On the freighter, as the team races through the decks to the control room, an airlock opens and creates a sudden vacuum. Everyone escapes but Chakotay, who is struck by flying debris and beamed to sickbay.

As Torres works to reinitialize the power matrix in the control room, the Doctor finds tissue samples on Pelk that suggest a being is aboard the freighter that has adapted to the radiation. From Astrometrics, Seven of Nine scans for a lifeform blended in with the ambient toxins on the ship, and the creature is then revealed. Suddenly, it closes in on the team in the control room as gas envelops everything. Neelix and Fesek are attacked, but Torres keeps the creature at bay and realizes it is a Malon core laborer.

The laborer insists sabotaging the ship is the only way to make the Malon understand how horrifying the radiation poisoning is to the men who sacrifice their lives working on the core. As Voyager emits a series of tractor pulses to steer the freighter into the star, the laborer uses maneuvering thrusters to disrupt its course. Torres tries to reason with him, but ultimately she has to resort to violence to stop him. At the last second, Torres, Neelix and Fesek are beamed to Voyager before the freighter explodes into the star's atmosphere.