Four days before Christmas in 1920, Dorothy Mort shot her lover dead in cold blood. The tragic end to her affair with dashing young doctor, cricket star and War hero, Dr Claude Tozer, scandalised Sydney. Dorothy's respectable husband was devastated. Following a trial that mesmerised the public and sent the media into a frenzy, the troubled North Shore mother of two and budding actress was declared 'not guilty on the ground of insanity'. After nine years in Long Bay Gaol, Dorothy was released and returned to live quietly with her husband . . . But was she really mad, or bad, or neither? And what was the secret that her husband kept for the rest of his life? In an absorbing blend of investigative non-fiction and biography, Suzanne Falkiner delves into the case that has intrigued Sydney for almost 100 years.