Captain Scarlet and the Mysterons - Season 1 Episode 29 : Traitor 1968

The Australian Spectrum Hovercraft Centre, Koala Base, the university-style academy where several trainees are sent to brush up their skills and sit their practical and mental exams to become Spectrum hovercraft pilots, is the most likely place for Captains Scarlet and Blue to investigate, where several explosive sabotages have been made upon Koala's state-of-the-art hovercrafts, hence why the Mysterons latest threat states that there is a traitor within the world-security organisation, and that it threatens to tear it apart from within. Already settling on a few probable suspects, including the cadet leader, their suspicions rise even further when their room is set ablaze when sleeping. But when attending a routine test-run the next day, with one of their selected suspects, the duo discover that there isn't any traitors within Spectrum at all.