Based on the first of the 'Boysie Oakes' novels by John Gardner, published in 1964. There were seven more: Understrike (1965), Amber Nine (1966), Madrigal (1968) Founder Member (1969), The Airline Pirates (1970), Traitor's Exit (1970) and Killer for a Song (1975). After that, Gardner took over writing the James Bond series from the late Ian Fleming.
The title song was sung by Shirley Bassey who had recently sung the title song for the James Bond film Goldfinger (1964).
MGM originally planned a series of Boysie Oakes spy pictures, but this fell through.
Composer Lalo Schifrin intentionally composed the score so it would not emulate John Barry's style from the James Bond franchise.
Apparently, star Rod Taylor insisted he play his character Boysie Oakes with an American accent because he was more comfortable with it by that stage in his career. Conversely, the Los Angeles-born Jill St. John employs a British accent.