Kes (Jennifer Lien) reacts poorly to Tuvix as his existence deprives her of both Tuvok and Neelix, her mentor and boyfriend respectively.
Two weeks after the accident, the Doctor (Robert Picardo) develops a contemporary equivalent to barium sulfate (BaSO) radiocontrasting using a custom radioisotope with which he can identify the disparate DNAs of the two original crewmen and use the transporter to disentangle the two.