Good and evil are so close as to be chained together in the soul.”
Written decades before Freud created the concepts of the ego and the id, there was an ordinary man living his ordinary life as a doctor. But his own experimental drug, meant to separate the two sides of human nature—good and bad—unleashes his evil persona, which then dominates his entire self. Murders happen, he loses control of himself and he has to choose: humanity or calamity. That is, if he isn’t already drowning in his own insanity.