While Frane is visiting the world of the Mari, he bumps into Torres in the marketplace. During interrogation, Torres confesses to Chief Examiner Nimira about her plan of hurting Frane.
Torres is advised to undergo engramatic purge, a medical procedure that aims to identify and remove offensive images from her mind. Janeway, however, protests when she has heard about the risk of neurological damage. Together with Tuvok, Janeway sets out to examine the evidence; they have discovered that Frane is previously arrested for harbouring violent thoughts.
Nimira claims that he has been cured through past purging.
At the market place, a Mari woman experiences Torres' extreme cruel thought against Frane and attacks and kills a young merchant.
Baffled by the two related attacks, Tuvok makes a probe; he has learned that a Mari named Guill has approached Torres after the incident. When Tuvok asks him, Guill senses telepathically the dark impulse of the Vulcan and offers a help to Tuvok to control them. However, Tuvok senses that Guill is having a business interest in violent thoughts after witnessing that Guill covertly accepts money from a fellow Mari.
Asking him further, Tuvok learns that Guill is buying violent thoughts as what he has done to Torres; however, Guill denies it. When Tuvok is about to bring him to Nimira for further interrogation, Guill's two conspirators capture them.
Meanwhile, Torres began his engramatic purging.
Tuvok brings Guill to Voyager. Janeway, however, gets Nimira to stop the purging process on Torres after Tuvok has explained that Frane and Guill conspired in order to provoke Torres's thought.