In Britain, where this series was made, Jack Hawkins was the top-billed of the show's four stars, but in America, he was second-billed to Dan Dailey.
The series had almost nothing in common with the Edgar Wallace novel from which it derives its title. In the novel (first published in 1905 and filmed by Ealing Studios in 1939), the "four just men" are a mysterious group of assassins. One of them is surnamed Manfred, like the Jack Hawkins character in the TV show, but the forename is different; the other three are called Poiccard, Gonzalez and Thery. The last-named is a small-time crook who is blackmailed by the other three into assisting in the murder of a reactionary cabinet minister.
Both Frank Thornton and Arthur Gomez were frequently employed as bit players in this series, sometimes appearing without credit and never playing the same role twice. Thornton was in twelve episodes and Gomez was in fourteen.
In his autobiography (published posthumously), Jack Hawkins noted ruefully that Sapphire Films, the company which produced this series for ITV (and which had had great success over the previous few years), went bankrupt soon after it was aired.