When the goddaughter and namesake of Florence Nightingale is found on a train to Hastings with her skull caved in, the subsequent investigation and public outcry fail to catch the killer. Driven to distraction by the absence of justice, Florence's partner of twenty-six years - Mabel Rogers - turns to Agatha in the hope she can succeed where the police failed. But pursuing a plan based on everything she's learnt through her work, Agatha discovers that this killer is far more cunning and dangerous than any of her fictional creations.