When Highsmith’s friend Arthur Koestler committed suicide with his wife due to his leukaemia and Parkinson’s disease, she was both shocked and furious. Her friend Jonathon Kent recalled, ‘As she talked about it her face blackened, and she was very angry. She said that she would never forgive him’. This chapter explores how Highsmith approaches the question of suicide in her writing, and examines how suicide or self-murder, perhaps the darkest of acts, accesses the Gothic in ways not usually considered within the context of crime writing. Emphasis will be placed on the ways in which the theme of suicide both foregrounds crime fiction’s debt to the Gothic and also provides an interdisciplinary presence that binds both genres together.