In 1895, Sidney Reilly had an affair with Ethel Lillian Voynich, a married Russian author. In 1897, Voynich wrote a popular novel, "The Gadfly". It was rumored that the adventurous hero of the novel was based on Reilly. In 1956, the novel was made into a movie, and Dmitri Shostakovich was commissioned to compose the music. The same music, "The Gadfly-Romance", is heard as the theme to this show.
The series takes place from 1901 to 1925.
Director Martin Campbell went on to a major Hollywood career including directing two James Bond films (GoldenEye and Casino Royale).
Sam Neill would himself do a screen test for the role of James Bond. This can be seen on the DVD for The Living Daylights.