[2] The show starred an American actor, Steve Forrest, as John Mannering, an antiques dealer who drives a Jensen C-V8 with 'BAR 1' as the distinctive, personalised number plate.

'The Baron' is portrayed as an occasional undercover agent working in an informal capacity for the head of the fictional British Diplomatic Intelligence, Templeton-Green (Colin Gordon) assisted by Cordelia Winfield (Sue Lloyd) and David Marlowe (Paul Ferris).

By transforming the character into an eligible bachelor and casting a Texan in the role, the producers decided that 'The Baron' would be nicknamed after the cattle ranch once run by his grandfather, described as being "200,000 acres [809.371 km2] 300 miles from Dallas".

For the TV series, Mannering's persona is depicted as absolutely straight with no suggestion of past criminality, a fact underlined by his being co-opted by British intelligence.

[2][3] Although not regular cast members, Reginald Marsh and Derek Newark also appeared in three episodes (once reprising earlier roles, and once playing different characters).

Occasionally, actors were used twice but in different roles in the same run of episodes, including Paul Maxwell, Peter Bowles, George Murcell and Edwin Richfield.

The character of Mannering was, like Simon Templar in The Saint, a member of the jet set, whose glamorous lifestyle was typified by air travel to exotic locations, which at the time was still only easily available to the wealthy.

The backlot at Elstree in particular was extensively used, being transformed alternately into Mannering's antiques shop, a Mexican town, a Parisian nightclub, an East European police station and many others besides.

Roy Ward Baker stated that owing to US sponsorship by a cigarette company, characters "were allowed to light up only in moments of leisure, never when they were frightened or under duress".