Neville retells the story of Thomas Edison declaring alternating ("indirect") current impossible, only for Nikola Tesla to have already proved it in his mind's eye and built a working model requiring no changes when it went to the factory. He casts Edison's doubt as playing the role of "Satan" -- not evil, but doubt itself -- to illustrate that any voice denying what one can imagine, however brilliant or authoritative, plays the same part, and that Tesla's answer, "Get behind me, Satan. I've done it," is the right response to it.