The series followed Father Stanley Unwin, a character voiced by (and modelled on) the comedian of the same name, who also played the character in live-action long-shots. Ostensibly an eccentric vicar, Unwin is secretly an agent of B.I.S.H.O.P. ("British Intelligence Service Headquarters, Operation Priest"), a division of British intelligence countering criminal and terrorist threats. Aided by fellow agent Matthew Harding (who works as Unwin's gardener in The Masquerade), the two undertake missions which require the Minimiser, a device used for covert operations which shrinks people to a third of their size (roughly the size of a Supermarionation puppet, which allows puppet characters to interact with live-action sets and actors whose faces are out of shot). Unwin carries the miniaturised Matthew around in a specially-adapted briefcase that can open from the inside and contains field equipment such as a periscope. During missions, the agents communicate via earpiece transceivers (with Unwin's disguised as his hearing aid). In hostile situations, Unwin regularly spouts gibberish (based on the real Unwin's nonsense language, "Unwinese"note ) to distract his enemies. The cast is rounded out by Unwin's housekeeper, Mrs. Appleby (who is unaware of his espionage activities), B.I.S.H.O.P.'s spymaster, known only as The Bishop, and BISHOP agent Blake, who is often called in to assist Unwin and Matthew on missions.
The series only lasted 13 episodes before being cancelled after Lew Grade saw a test screening, believing that the inclusion of Unwin's "Unwinese" had made the series impossible to sell internationally (indeed, it was a tough sell domestically, only three ITV regions aired this - ATV, Granada and Southern). As a result, Anderson shifted full-time into live-action with UFO (1970), and wouldn't make another puppet series until Terrahawks 14 years later.
The Secret Service provides examples of the following tropes:
- All Just a Dream: "Errand of Mercy"
- Cool Car: Gabriel, Father Unwin's yellow Model T Ford.
- Fun with Acronyms
- Medium Blending: A mix of Supermarionation blended with live-action set-pieces, sets and actors (with their faces obscured).
- Neologizer: Father Unwin's "Unwinese", a trademark of the real-life Stanley Unwin's comic act.
- Shrink Ray: The Minimiser, primarily used to shrink Matthew to enable him to move around in secret. In addition, in "A Case for the Bishop" Unwin uses the Minimiser as a demonstration of power by shrinking the Dreisenberg Ambassador in order to force him to give back the computer he stole, and in "More Haste, Less Speed", the Minimiser is used to shrink Unwin, Matthew and Gabriel (exactly how is unclear, since it's done off camera) to enable them to better covertly observe the episode's villains.
