A crewmember named Darwin is found dead and an investigation soon reveals murder. It is discovered that Lon Suder, a Betazoid, killed him, because he did not like the way Darwin looked at him.
To discover the reasoning behind Suder's admittedly senseless act, Tuvok initiates a mind-meld with Suder. This causes Suder's violent impulses to be transferred to the Vulcan, giving Suder a sense of calm by causing Tuvok to experience uncontrollable violent urges himself: he even attacks a holographic form of Neelix. Eventually, Tuvok confines himself to quarters, and removes himself from duty as he is unable to control his violent urges. The Doctor attempts to cure Tuvok of his urges by forcing his emotions into the open. This fails, and Tuvok is able to escape. He finds Suder with the intent of executing him, hoping this will satisfy himself. Tuvok is convinced by Suder not to kill him and instead mind-melds in an attempt to get his emotional control back. This meld renders Tuvok unconscious, allowing Suder to notify the crew. Later, the Doctor watches over Tuvok, hopeful that since he controlled himself enough to not kill Suder, he is recovering.