In September 1940, as Britain faced an imminent Nazi invasion, handpicked groups of ordinary men – known as scallywags – were trained in top secret to act as saboteurs and assassins. In a new series of wartime thrillers, author V.M. Knox has created the character of Clement Wisdom – a humble East Sussex vicar – called upon to lead a local team of scallywags, creating a tension between his faith and his patriotic duty. V.M. Knox talks to Rob Weinberg about her novels, in which historical fact meets crime fiction and the murky world of espionage.