Mike McCarthy worked as constable in the New Zealand police, but was promoted to Detective Sergeant some time after 1970. After Ted West's crew were released from prison after the Smith & Caughey's job, he would wind them up, making them suspect each other of ratting them out. He made Bert Thompson his informant in exchange for pay, which might also have been the reason for his early release.
Mike drove Ted home after his release from prison coinciding with the Commonwealth Games of January 1974, and gave him back his bag which he used on the job. After a robbery of Philips K9 television sets, Mike questioned Ted as he had recently been released from prison. He flattered Ted by saying he was a hard man to crack and Lefty Munroe didn't have a patch on him. When the Wests moved house, he inquired Bert and kept the house under surveillance.
Mike is introduced when Wayne Judd buys into his private investigation business. The two knew each other from when they were cops and get on well. They set out on jobs together such as following Ted. Mike dies after two episodes from a heart attack and Judd purchases his business.