The novel told the story of former WWII resistance fighters who were individually known by animal-based code names and collectively as 'The Zoo Gang'. They reunite when they find a lead to one of their former colleagues who betrayed them to the Gestapo, the appropriately code-named 'The Wolf'.
Grade took the basics of that plot for the first episode, penned by famed scriptwriter Reginald Rose, but changed the nationalities of the majority of the gang from their original French to appeal to the UK/US market; so we had John Mills as the British Tommy Devon ('The Elephant') Brian Keith as the American Steven Halliday ('The Fox') Barry Morse as the Canadian Alec Marlowe ('The Tiger') and Lilli Palmer as Manouche Roget, now the only French character ('The Leopard')
The show lasted for just one series of six hour long episodes featuring our geriatric heroes battle vice, corruption and robbery on the Cote d'Azur. It had much promise, but ultimately the scripts weren't up to much; indeed John Mills even suggested strike action at one point to demand better material!
As with many ITC series, the theme tune was eminently catchy and a pretty funky accompaniment to the excellent opening titles. It was provided by former Beatle Paul McCartney and his wife Linda in the guise of their then band Wings. It featured as a B-Side to Band On The Run