Gunn operates in a gloomy waterfront city, the name and location of which is never revealed in the series. He can usually be found at Mother's, a smoky wharfside jazz club that Gunn uses as his "office", usually meeting new clients there. His standard fee is $1,000 but it can be more, less, or nothing, depending on the client or the circumstances. Gunn has a reputation for integrity and being among the best investigators; he has many reliable informants and is extremely well-connected. His reputation is so good, the police occasionally ask "him" for help or advice. He sometimes works cases out of state and occasionally out of the country. Gunn was observed by a female character named Rowena in "Murder on the Midway" as "wearing $30 shoes, a $200 suit and carrying a solid gold cigarette lighter". Gunn drives a 1958 two-tone DeSoto two-door hardtop in the first few episodes of the first season, then a 1959 Plymouth Fury convertible with a white top and a car phone. In the third season Gunn drives a 1960 white Plymouth Fury convertible with a car phone, later changing to a 1961 Plymouth Fury convertible.