The series title relates to the character of Michael Ryan a dashing private investigator played by Rod Mullinar. (A few years prior Mullinar had briefly taken the lead role in similar Crawford's series Hunter (1967) in its closing episodes after the original lead actor Tony Ward left the show.) Ryan's assistant Julie King was played by New Zealand-born actor Pamela Stephenson, soon to leave for England and a successful television career. Other regular characters were Tony Angelini (Luigi Villani), a taxi driver and Ryan's regular informant, while Detective Cullen (Colin McEwan) was Ryan's main liaison with the police force.