The series was a spin off of the television series Department S (1969) and featured Jason King played once again by Peter Wyngarde. In Department S, King was a dilettante dandy and author working as part of a team of investigators. In Jason King he had left that service and was concentrating on writing adventure novels following the adventures of the fictional Mark Caine, [which the Jason King character was also writing about in Department S] who closely resembled Jason King in looks, manner, style, and personality. None of the other regular characters from Department S appeared in this series. The series had a single season of 26 episodes.
In the course of visiting international locations as part of his research, or through being summoned by people needing assistance, King would be frequently embroiled in adventure stories featuring glamorous women, exotic locations, menacing villains, political turmoil, or espionage intrigue.
The first episode depicted King’s retelling of a Mark Caine novel to a television executive, alternating between King’s interpretation of events, and the television executive’s version. King’s version showed style and class, while the executive’s version featured added suspense, more cliches, and had the women in more revealing costumes. In the footage representing both men’s vision of the novel adapted for the screen, Mark Caine was portrayed by Wyngarde.