Thomas Edison (Benedict Cumberbatch) comes up with an amazing new invention – the lightbulb. George Westinghouse (Michael Shannon), who has been powering homes and buildings with gaslight, comes up with a way to provide electric lighting to more homes using alternating current (AC), instead of direct current (DC), which Edison has created. He is hoping to partner with Edison in combining his cheaper system with Edison's lightbulbs in order to provide not just the rich, but everyone, with this wonderful new innovation.
Enraged that Westinghouse is trying to jump in on his idea, Edison denounces AC, saying it is dangerous and will kill people. To illustrate this, he hooks a horse up to AC current to show how the current can kill. However, the quick death of the horse inspires people to realize electricity can be used to kill people on death row, and they decide to come up with an electric chair, something which Edison is very much against, having said he would not make anything that could be used to kill people.