- You may be looking for the planet.
Chief Inquirer Tarron was an investigator in the city of Millennius on Marinus. He arrested Ian Chesterton for stealing one of the keys to the Conscience of Marinus and murdering Eprin. He later walked through the events with the First Doctor, who was defending Ian, and Barbara Wright and Susan, who were serving as his "detectives." (TV: The Keys of Marinus)