On a planet of giant genetically modified tribbles, the crew hunts bosonite while Zero learns their body is failing.
Needing bosonite to build a new proto-core, the crew lands on a planet overrun by giant, genetically modified tribbles. Zero breaks a leg and learns that their body is deteriorating and will not last much longer. Rok-Tahk works with the Klingon scientist who accidentally created the creatures to reverse the mutation, but in the process she produces a new hybrid, nicknamed a bribble, which she adopts as a pet.
With the bosonite in hand, the crew builds the proto-core and sets a course to rejoin Voyager-A. The episode plays the franchise's famous furry pests for comedy by scaling them up to monster size, while Zero's diagnosis plants a serious thread that pays off when Zero later sacrifices their failing body to save Voyager. Rok-Tahk's scientific curiosity again drives the solution, as it has throughout the series. Keith Sweet II wrote the episode.