The Federation starship Voyager is orbiting the Mari homeworld, a race of telepaths. As the ship's crew trade for supplies, they find it difficult to haggle and bargain with mind readers. While all of this is happening, Lt. Commander Tuvok and the city's Chief Examiner, Nimira, talk about security and maintaining order. Nimira states that her job is slowly becoming obsolete with their methods of crime prevention. There has been no violence in their society for years, and she is one of the last security officers among the Mari. Sharing a curiosity regarding crime and punishment in their own society, Tuvok offers to transport her aboard Voyager to demonstrate their ways of security enforcement. While Captain Janeway and her half-Klingon Chief Engineer B'Elanna Torres are negotiating for a resonator coil, someone bumps into Torres, momentarily irritating her. She calms herself, shrugging it off as an accident. Moments later they run over to find the man who bumped into Torres beating another man bloody. The beaten man is severely injured as Janeway stops the aggressor. The aggressor seems surprised at himself and says he does not know why he did that. While aboard Voyager, Namira is puzzled about the ship's brig and the concept of incarceration as a form of punishment, only to be called back to the surface regarding the attack. After questioning the crew, Nimira, the Mari constable, determines that B'Elanna's angry thought earlier that day was transmitted telepathically to the aggressor, and thus she is the more guilty of the two. She is sentenced to undergo memory modification to remove the thought, as is the aggressor. Janeway protests, as the modification process carries the risk of neurological damage. Before Janeway can unearth enough evidence to try to get Torres out, another attack occurs with the same memory, indicating that it is still in circulation. Unfortunately this attack ends with an old woman plunging a knife into the body of an attractive young woman that Neelix had become enamored of. Voyager's Vulcan Security Chief Tuvok goes undercover and finds an illicit memory trade in which the salesman of the resonator coil is a key figure. He determines that B'Elanna's memory was goaded from her in order to be resold, but it was too violent for the illicit Mari tradesmen to contain, and this caused the outbursts among the Mari. Torres is released due to this new evidence, just moments before her brain was to be probed. Nimira herself is shocked to find that all thoughts of violence have not disappeared from her people.

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