Anthropologist and prehistorian Prof. Dr. Crusius, accompanied by his assistant Karl Mill, is tracing the footsteps of early humans. He aims to prove the existence of a human being from a hundred thousand years ago. Furthermore, he is convinced that an animal soul resides within every human being. He faces hostility because of his theory and receives anonymous threatening letters. He delivers a major lecture before the anthropological society. Ultimately, the professor is even forced to fight a duel with an adversary over his hypothesis.