"Traitor!" is the twenty-ninth episode of Gerry Anderson's Captain Scarlet And The Mysterons.
A series of hovercraft crashes at the Spectrum Organisation training academy, Koala Base, is followed by Mysteron claims of a traitor amongst Spectrum personnel. This motivates its superintendent, Major Stone, to ask Colonel White for assistance. The Colonel dispatches Captain Scarlet and Captain Blue there, ostensibly as guest lecturers.
After he and Captain Blue, together with some Spectum trainees, take a hovercraft out onto the outback, where it overheats and leaks oil, Captain Scarlet barely manages to rescue its "black box," or operations recorder, before being killed in the crash--and, as has become usual for him, retro-metabolising afterwards. It reveals that the "traitor" is, in fact, a part common to all the Spectrum hovercraft deployed to Koala Base, all examples of which the Mysterons took over at the manufacturing plant.