It's 1919, and Louisa Cannon dreams of escaping her life of poverty in London, and most of all her oppressive and dangerous uncle. Louisa's salvation is a position within the Mitford household at Asthall Manor, in the Oxfordshire countryside. There she will become nurserymaid, chaperone and confidante to the Mitford sisters, especially 16-year-old Nancy - an acerbic, bright young woman in love with stories. But then a nurse - Florence Nightingale Shore, goddaughter of her famous namesake - is killed on a train in broad daylight, and Louisa and Nancy find themselves entangled in the crimes of a murderer who will do anything to hide their secret.