Everyone in the UK knows the eccentric Williamson sisters Penny and Josephine. At over 90 years old, they are among the last living war veterans in the kingdom. For the gallery owner Archie, they are the beloved great-aunts from whom he has learned everything important in life. From fly fishing and changing tires to the recipe for the perfect martini. When the two ladies are to be honored in Paris, he packs his bags without further ado to accompany them. And so begins a journey into the past, to the outbreak of war, to a tragic love story and the secret missions that Penny and Josephine have carried out for the British government. Because contrary to what Archie believes, his aunts are by no means harmless senior citizens. And in Paris they still have a score to settle ...