Flack runs an old style hardware store in Great Worthy and also acts as landlord, renting out a cottage to two young women. This feeds into his hobby, as he had made several peep holes about the property to further his peeping tom tendencies.
After one of the young women is killed, DCI Barnaby finds at least one of Flack's peeps to the downstairs bathroom, and questions him. Unable to stop, he continues to peep at the second young woman, Jo, and was on hand when the murderer finally returned and smashed down he door with a sledge.
Flack ran off to flag down a police car, saving Jo's life and enabling the capture of the killer.