Sally Meredith is in deadly danger after her mercurial uncle “Fritzi,” the genius chemist and inventor M. Frederic Lasalle, disappears into the night. He leaves her as the only person who knows how to open the Chinese puzzle box in which he has concealed the formula for his latest invention: a new gas, sudden, swift, and deadly beyond anything ever before devised. Soon, Sally is in the clutches of sinister foreign agents, and her former fiancé Bill Armitage, of the War Office, with the aid of a Scotland Yard detective, desperately searches for her …