Department S is an elite branch of Interpol, headquartered in Paris. They are called in when a case has no logic or solution and the "regular" police investigations have run into dead ends. Sample cases include a jet landing in London with no passengers or crew aboard, a man in a space suit found dead in Soho, and an assassination of a wax dummy. The team consists of three operatives, each one with a different approach to solving cases, plus the official head of the Department.
Stewart Sullivan (Joel Fabiani) is the field leader of Department S. A former FBI agent, he knows every seemingly ridiculous case has a logical explanation, and he uses his intelligence to sort through the clues to find it. While he relies primarily on his brains, his fists are also useful weapons when he has to fight. He and Annabelle obviously had (or are continuing) a romance (although it is never shown or directly referenced).
Jason King (Peter Wyngarde) is a best-selling novelist. His books depicting the adventures of his fictional creation, Mark Caine, have sold "60 million books in 15 languages" according to Sir Curtis. Jason's approach to a case is completely different: he theorizes the most outlandish scenario imaginable, then treats the solution the way his fictional hero would. He is a playboy who is easily distracted by a pretty face.
Annabelle Hurst (Rosemary Nicols) is a computer expert. Much like her computer, nicknamed "Auntie", Annabelle sees cases strictly in black and white. She has little patience for Jason's wild theories (although Stewart reminded her once that Jason "has a nasty habit of scoring near-misses" with his outlandish ideas). Yet the sole woman of the Department is not confined to the office, she works the field as well.
Sir Curtis Seretse (Dennis Alaba Peters), a high-ranking diplomat from an unnamed African country, is the official head of Department S. He decides which cases will be handled by the Department (which occasionally finds him butting heads with Stewart). Because of his status he is able to avoid red tape and get top secret information that would otherwise be out of the Department's reach. His diplomatic position sometimes causes him to become part of the case the Department is trying to solve, and on occasion he even helps out in the field.
Department S originally aired in the UK from 1969-70, then was syndicated worldwide, earning fans wherever it played, and still has a loyal following.