When the body of a crewperson named Darwin is found in Engineering, everyone assumes his death was accidental — until the Doctor determines that Darwin was, in fact, murdered. Tuvok launches an immediate investigation. A check of engineering logs places a Maquis named Suder at the scene of the crime. At first, Suder denies being involved. But when DNA evidence implicates him, Suder confesses, telling Tuvok he killed Darwin because "I didn't like the way he looked at me."

Unwilling to accept such a senseless motive for such a serious crime, Tuvok interrogates Suder in greater detail. To Tuvok's dismay, Suder can't articulate what drives his violent outbursts, so Tuvok secures his permission to perform a Vulcan mind-meld. Tuvok hopes it will help him understand Suder's motivations, and that some of his own Vulcan self-discipline will rub off on the confessed killer, allowing him to better control his violent nature.

Tuvok briefs Janeway on his mind-meld with Suder, and they discuss punishment options. Tuvok admits that although Suder seems calmer since the meld, he finds himself feeling disconcerted. Later, an encounter with the playful Neelix so enrages Tuvok that he strangles him; fortunately, the event occurs only in Tuvok's holodeck program.

Tuvok meets with Suder, who unsettles Tuvok with his comments about the seductive lure of violence, which Tuvok now fully understands. Fearful of his own impulses, Tuvok seals himself in his room and tells Janeway he's no longer fit for duty.

Janeway sends Tuvok to Sickbay, where he starts undergoing treatments to control his violent tendencies. That evening, Tuvok breaks out of Sickbay and confronts Suder, saying he's come to execute him. Yet Tuvok's rational instincts prevent him from completing the act of murder, and he collapses. Suder summons help and Tuvok returns to Sickbay where he successfully completes his rehabilitation.