"As long as I can't be at home, I'd rather be here than anywhere in the world I can think of!" Was it little more than a week, thought Harry Fleming, American Boy Scout living in London, since he had uttered those words so lightly? Was it just a week since Grenfel, his English scoutmaster, had bidden the boys good-bye? Was it just two days since father and mother had been so suddenly recalled to the States? Was it just that very morning that he and his good chum Dick Mercer had been detailed on this mission which had led to the discovery of the secret heliographs so busily sending messages to the enemy across the North Sea?