Private detective Cormoran Strike is approached by a worried father whose son, Will, has joined a religious cult in rural Norfolk. At first glance, the Universal Humanitarian Church seems to be a completely peace-loving organization advocating for a better world. Yet, as Strike digs deeper, he discovers that there are sinister implications and unexplained deaths lurking beneath the surface. To try to save Will, Strike's business partner Robin Ellacott decides to infiltrate the sect and travels to Norfolk to live among them incognito. However, at the same time, she turns out to be unprepared for either the dangers that await her there or the losses that this will bring her...