The central theme of Mary Midgley’s Wickedness: A Philosophical Essay is that the traditional analysis of evil as a privation is correct. Midgley adapts and adopts this analysis of evil as something good gone bad, as a parasite feeding on goodness. In this view, the notion of a completely evil world is logically inconsistent; evil cannot occur save as the perversion of something good. This view has Platonic and Augustinian sources. In Wickedness, the view that evil is to be seen as something good gone bad is developed and defended in connection with evolutionary theory and a rather Aristotelian view of human nature. The major opposing views are described and critiqued.