One of those FAQs of writers, directors, producers is “Where do you get your ideas from?” which always sounds as if there is a magic ideas tree from which creatives can harvest the fruit when needs want. In truth, ideas come from the most unlikely of sources—from dreams to the sayings of some well-beloved aunt. When Gerry Anderson, the producer and director of the hit puppet shows as Supercar, Fireball XL5, and Stingray, was thinking up ideas for his next series, his imagination was captured by the tragic events of a mining disaster in Germany. In October 1963, a discharge lake situated over the Lengede-Broistedt mine flooded the shafts and tunnels deep underground. 129 workers were trapped by the flood water. During the first few hours, 79 of the miners managed to escape by climbing ladders in the mine’s ventilation shafts, but there were still 50 miners unaccounted for. Just when the rescuers had almost given up hope of finding the missing miners, a metallic sound was heard tapping out a signal deep underground. A small bore hole was drilled and microphones lowered to communicate with those miners trapped more than 190 feet down. It was then decided the only way to...