Secret of the Dragon's Scales continues the adventures of Gavin Kane, Emily Scott, and Bunty Digby, fifteen-year-olds who make the best of their young lives in England during the autumn of 1943. World War II rages on, but the tide seems to have turned in favor of the Allies. Three times previously, the teens have defeated Nazi plans to defeat England using evil magic, and three times, there have been new alliances formed with creatures from the hidden worlds of legend and fable. Yet once again, Heinrich Himmler is determined to unleash another strange and horrible weapon from deep within Nazi Germany, while halfway across the world, Allied armies are now tenaciously fighting the Japanese Empire.
Secret of the Dragon's Scales continues to develop the ongoing influence of Thaddeus Osbert. The dragon has become indispensable in assisting his teenaged charges, as they inadvertently aid the Allied efforts against Nazi Germany. However, the dragon also takes quite seriously his responsibility to instruct Gavin Kane in the ways of justice, honor and above all - compassion. Sir Osbert manages to negotiate a steady source of sugar for his persistent sweet tooth, in exchange for supplying something Winston Churchill needs as well. Once again faced with danger and intrigue, the teens call upon their dragon friend to help them battle the Nazis, who finally commit their own winged monstrosity, with unexpected results.