“All irregularities will be handled by the forces controlling each dimension. Transuranic, heavy elements may not be used where there is life. Medium atomic weights are available: Gold, Lead, Copper, Jet, Diamond, Radium, Sapphire, Silver and Steel. Sapphire and Steel have been assigned.”
-Opening non-explanation for Sapphire and Steel
Sapphire and Steel was the real vehicle for terror in my childhood. Never mind hiding behind the sofa. This was a programme to be watched through a crack in the door from the next room.