The law enforcement body of the Mari, a telepathic people who have outlawed violent thought, which arrested B'Elanna Torres for a moment of anger that led to an assault.
The Mari Constabulary keeps the peace on a world where crime has almost vanished because aggressive thoughts themselves are illegal. Offenders are treated with an engrammatic purge that removes the offending images from the brain.
In Random Thoughts, Chief Examiner Nimira investigates a beating in the market and traces its cause to Torres, who had a flash of temper when a Mari named Frane bumped into her. The thought passed to him and drove him to violence. Torres is sentenced to the purge despite the risk to her mind, and soon afterwards another borrowed thought leads to a killing.
Tuvok, working alongside Nimira, finds that a trader called Guill deals in forbidden violent imagery and had taken the thought from Torres deliberately. He exposes the trade through a mind meld, and Nimira halts the procedure.