No enemy but time...

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!

Big Finish's series of full-cast audio dramas on CD, starring Susannah Harker and David Warner as mysterious time detectives, Sapphire and Steel.