Fleeing a disastrous affair with a colleague, Isabel Henley leaves the US to begin a PhD in Scotland. There she reconnects with the charismatic scholar Rose Brewster, a former classmate, who becomes a much-needed friend. When Rose reveals she’s in trouble, Isabel decides to help her. Then Rose vanishes. At first it seems she has taken her own life, but then Isabel receives a coded message: Rose is alive but held captive by people who don’t want her to complete her research. Isabel realises she must finish it if she wants to save her friend’s life – and her own. Isabel’s search takes her to Italy and France where she uncovers a chain of betrayal and treason lasting centuries. She must solve a 400-year-old mystery – or risk being claimed by it too.