The Enemy of the World is the only story in Patrick Troughton's 'Monster Season' that doesn't actually feature any monsters.
It does, however, have some men with funny hats and strange black PVC outfits in it.
Location for the story took place at Climping Beach near Littlehampton, West Sussex - not quite as good as sunny Australia, but close, and only a few miles form the Arundel Castle location used just over 20 years later for Silver Nemesis.
The Enemy of the World features footage of an exploding helicopter, taken from the Bond movie From Russia With Love.
Patrick Troughton's son David makes his first appearance in Doctor Who, as an extra in episodes five and six. David went on to play a soldier in The War Games and King Peladon in The Curse of Peladon.
Another Doctor Who debutant was director Barry Letts. After starting his career as an actor, Letts turned to scriptwriting in the 1960s. He'd previously submitted story ideas to the Doctor Who production office, but these were not taken up.
After taking the BBC's internal directors' course in 1967, Letts worked on Z Cars and The Newcomers before getting his first Doctor Who assignment with The Enemy of the World.
Barry eventually became the show's producer throughout the Third Doctor era, and briefly returned as Executive Producer to oversee Season Eighteen - John Nathan Turner's first as producer.
George Pravda, who played Denes, went on to portray Jaeger in the Mutants and Castellan Spandrell in The Deadly Assassin. Milton Johns (Benik) also went on to play a Castellan - Kelner in The Invasion of Time. Small Universe, isn't it?
The Enemy Of The World was the final story overseen by producer Innes Lloyd, who went on to produce The Stone Tape and Talking Heads for the BBC. Lloyd was replaced by his story editor Peter Bryant, with Derrick Sherwin taking over Bryant's job.
Of the six episodes, only episode three still exists in the BBC's video archives. It was released on the compilation tape The Troughton Years. Audio recordings exist of all six episodes, however. These were released by the BBC Radio Collection in August 2002, with new linking narration from Frazer Hines.
Sadly for Photonovel fans, the telesnaps of episode four do not exist. We are therefore presenting a simplified version of the episode using other images from the story to illustrate Marcus Hearn's captions.