Inspector Quillon was a policeman on Tairngaire.
He went with the Seventh Doctor, Ace, Benny and other Tairngaire experts to investigate the origins of the duplicates on Arden. When Umbra later mentally controlled the people on the spaceship, Ace was unaffected as she had been duplicated by benevolent Shenn so her real mind was still on Arden and out of range. She killed Quillon, who had picked up a stun gun and was sweeping it over everyone. She was never sure if he was being controlled, or he had managed to break free and was trying to help. (PROSE: Shadowmind)