Showing Miss Silver Intervenes by Patricia Wentworth

When her fiancé, Giles Armitage, is lost at sea in the middle of the Second World War, Meade Underwood is left in the company of a middle-aged aunt with nothing but a monotonous round of bridge parties and war work to fill her days. A chance encounter restores Giles to Meade but he has lost his memory, and their rediscovered happiness is threatened by the machinations of the scheming Carola Roland, a figure from Giles's forgotten past. So when Carola is viciously murdered, Giles becomes the chief suspect and it takes all Miss Silver's ingenuity to unravel the real significance of the crime and its electrifying consequences.