Viewers had to wait 13 weeks until the mysterious Voice of Truth was revealed in the spy series called Tightrope. This was one television series which was written specially for all espionage addicts. Victor Pemberton, who wrote all 13 episodes, dreamed up the idea for Tightrope after visiting a school in London. So Pemberton went away and decided to write a series involving a comprehensive school just like the one he had visited. In Tightrope, the U.S. Air Force base was the North Atlantic Treaty Organisation's communications center for a particular area of England. Spencer Banks —one of the stars of Timeslip—had a main part in Tightrope. He played a sixth-former called Martin Clifford who is more or less seconded by a mysterious character called Forrester as a junior detective. Each episode of Tightrope left viewers guessing—which wasn't surprising because, apart from American spies, there were agents of the Soviet secret service at work.