Plot summary
On stardate 49655.2, Lieutenant Tuvok (Tim Russ) and Neelix (Ethan Phillips) are sent to collect botanical samples from a class-M planet. When beamed back aboard Voyager, the two men and the orchids they collected are merged at the molecular level to become a single lifeform which names himself Tuvix (Wright). After ruling out transporter malfunction, the crew discovers that when demolecularized, the genetic material of the alien flowers acted as a symbiogenetic catalyst and is the culprit for the combination of the two crewmembers. Unfortunately, the process cannot be reversed, and Tuvix is accepted as a member of the crew with the rank of lieutenant, functioning as chief tactical officer in Tuvok's stead.
Kes (Jennifer Lien) reacts poorly to Tuvix as his existence deprives her of both Tuvok and Neelix, her mentor and boyfriend respectively. Her displeasure lessens over the course of the episode, but never completely eases. Captain Janeway (Kate Mulgrew) accepts Tuvix in his role as an excellent chief tactical officer and "an able advisor, who skillfully uses humor to make his points". Tuvix himself, having the combined memories and personalities of his constituents, melds the previously intractable qualities of both and improves upon them, flexing either muscle as the situation requires: "Chief of security or head chef, take your pick!"
Two weeks after the accident, the Doctor (Robert Picardo) develops a contemporary equivalent to radiocontrasting, using a custom radioisotope with which he can identify the disparate DNA of the two original crewmen and use the transporter to disentangle them. However, Tuvix denounces the procedure; he argues that he has rights, and to restore the two lost crewmen would require his execution. After discussing the situation with Commander Chakotay (Robert Beltran), Kes, and Tuvix himself, Janeway ultimately decides to proceed with the separation, acting in absentia to protect the rights of the two constituent men. Tuvix makes a final emotive plea for support from the crew, but finds no supporters. After the Doctor refuses to take Tuvix's life in compliance with the medical precept of doing no harm, Janeway performs the procedure herself and succeeds in restoring both Tuvok and Neelix.
Credits
Adapted from Wikipedia contributors, Tuvix. Paragraphs and formatting adjusted; illustrations, reference markers, block quotations and non-story material omitted.