Having reluctantly agreed to make up the numbers at a World War II-themed murder mystery weekend at Mortmead Hall, Anna Hopkins and her fellow dogwalkers, Isadora and Tansy, enjoy themselves far more than they'd expected. Not for long. The weekend's festivities come to an abrupt halt when a body is discovered floating in the ornamental pond.

Who was the mysterious woman in the red dress who attended the event without a ticket? As Anna and her friends delve further, they find themselves caught up in a web of intrigue that leads to a lost painting and a devastating wartime secret: a secret that involves Anna's own family. Was her late father really guilty of a monstrous crime ...?