The film dramatises events leading up to the 1857 trial of an otherwise-respectable young woman, Madeleine Smith (Ann Todd) for the murder of her draper's-assistant lover, Emile L'Angelier (Ivan Desny). The trial produced the uniquely Scottish verdict of "not proven", which left Madeleine a free woman. The film begins with the purchase of a house in Glasgow by an upper middle-class Victorian family. Their eldest daughter Madeleine claims the basement bedroom so she will have easy access to the servants' entrance and be able to entertain her lover, Frenchman Emile L'Angelier, without her family's knowledge.