When Naomi Klein discovered that a woman who shared her first name, but had radically different, harmful views, was getting chronically mistaken for her, it seemed too ridiculous to take seriously. Then suddenly it wasn't. She started to find herself grappling with a distorted sense of reality, becoming obsessed with reading the threats on social media, the endlessly scrolling insults from the followers of her doppelganger. Why had her shadowy other gone down such an extreme path? Why was identity - all we have to meet the world - so unstable?