“They could,” he said. “But we want to avoid that if possible. They are the result of immense thought, and no alteration would be as good. Besides, on one or two points change is simply impossible. Still, something could be done, I suppose, if it were absolutely necessary. But you see the difficulty, Hannay. Our enemies are not going to be such fools as to pick Royer’s pocket or any childish game like that. They know that would mean a row and put us on our guard. Their aim is to get the details without any one of us knowing, so that Royer will go back to Paris in the belief that the whole business is still deadly secret. If they can’t do that they fail, for, once we suspect, they know that the whole thing must be altered.”

“Then we must stick by the Frenchman’s side till he is home again,” I said. “If they thought they could get the information in Paris they would try there. It means that they have some deep scheme on foot in London which they reckon is going to win out.”