In the original script, the Graff did not murder the Seeker but instead sent her back to the Catacombs, whereupon the Captain set off the explosion to seal the caves (killing the Seeker in the process). Believing himself to be the prophecied survivor, the Graff - insane and hallucinating about past campaigns - then took an ammunition pouch from a supposedly dead guard. The Doctor would reveal himself at this stage while an explosion detonated, proclaiming the Graff's final end.
Anthony Read suggested that the jethrik be the first segment of The Key to Time. It was originally important, because it was actually a source of incredible energy which could power a fleet of spaceships.
This episode was watched by 8.2 million viewers on its original transmission.