Since 2015, hundreds of thousands of refugees have arrived in Germany, and the theory of the "great replacement" is circulating online: the country is said to be targeted for elimination by a global financial oligarchy using migration as a weapon. Alongside a lack of trust in politics, belief in conspiracy theories is a characteristic of the populist unrest. But what makes an explanation a conspiracy theory? Why are they so attractive to many? And what can be done about them? Answers to such questions are found less frequently than the conspiracy theories themselves. Michael Butter explains how such narratives work, where they come from, and what effects they can have. While these theories are always wrong because they underestimate the internal logic of social systems, they must still be taken seriously as a symptom. Currently, they serve as an indicator of the threat to democracy.