T'Pol, Sato and Reed land on a planet to investigate a Xindi landing craft, seemingly abandoned two weeks ago, and are infected with a virus that changes their DNA and urges them to return to their capital city. The virus was created by a dying race attempting to find an alternate way to reproduce. A ship of exterminators seeks to kill the infected crew to prevent an outbreak. Phlox develops a cure using T'Pol's DNA.
Originally broadcast on "Great Performances" (1972).