Phlox faces an ethical question on a planet with a dying species.
The episode is framed as a letter from Phlox to a human colleague, Dr. Jeremy Lucas, describing his life aboard Enterprise. The ship meets the Valakians, a species dying from a genetic disease, and Phlox searches for a cure.
He finds that the illness is part of their evolution and that another species on the planet, the Menk, may be poised to flourish once the Valakians decline. Phlox argues that curing the Valakians would interfere with natural development, and Archer reluctantly agrees, giving them only a treatment to ease their symptoms. The episode, often linked to the later Prime Directive, was directed by James A. Contner and written by Andre and Maria Jacquemetton.