Dear Doctor

Phlox composes a letter to a fellow doctor on the medical exchange, sharing his impressions of the curious humans around him. Enterprise meets a pre-warp ship from the Valakian people, whose world is being devastated by a plague, and Archer agrees to help. On the planet Phlox learns that a second species, the Menk, lives alongside the Valakians, is treated as inferior, and is unaffected by the disease. He discovers that the plague is genetic: the Valakians have reached an evolutionary dead end, while the Menk appear to be on the rise. Phlox finds a cure but argues it would be wrong to use it, since it would interfere with the planet's natural development. Archer reflects that one day there may need to be rules for situations like this. In the end they decide to withhold the cure, giving the Valakians only medicine to ease their symptoms for some years.