"There can be no doubt about the seriousness of the affair," I said. "The French Service have done very well so far, and so have our friends in London. We are quite well aware that during the past few weeks there has been an amazing recrudescence of German espionage, both here and in England, and even Whitehall is seriously alarmed. There is good reason for believing that working drawings of the new British trench-mortars have, by some means, been smuggled over to Germany. How they got out is a complete mystery, for the control at all the ports has been stricter than ever. Yet van Ekker has managed to get through to Holland a message from Berlin which leaves very little doubt as to the fact. It is undeniably serious, for the new mortar is a wonderful production, and I happen to know that it was intended to be one of the grand surprises in the Allies' spring offensive." Hecq grunted, and I paused. Then I went on saying: "We have a pretty good idea of the traitor in the department concerned, and he is now safely under lock and key. Unfortunately the mischief was done before he was even suspected, and the closest inquiries have failed to unearth any of his associates who would be regarded as in the slightest degree doubtful. It looks very much like a case of a hitherto thoroughly reliable man yielding to a sudden and overpowering temptation, while the real culprit--the man who pulled the strings-- remains undiscovered. No doubt Count Wedell and his precious propaganda department have a first-class man at work, and they have so cleverly covered up the tracks that the method of their latest coup remains a mystery. It is perfectly obvious that the subterranean work of Germany is even now proceeding in France, Italy, and Great Britain." "Exactly, _mon cher_ Sant. And you must take this particular matter in hand at once, and try to discover at least one of the fingers of what your good friends across the Channel call so appropriately `the Hidden Hand.' For myself, I feel quite sure that at last, after much seeking, we have alighted on the source of the whole affair, so far as England and France are concerned." Our conversation had taken place at Armand Hecq's house out at St Germain, beyond Paris. I had come post-haste from Lausanne, where I had been engaged with Poiry--an ex-agent of the Paris Surete--upon another matter. An urgent telegram from Hecq had warned me that the new business was most important, hence I had lost no time in answering his summons. It was a warm afternoon, and we were seated out on the terrace overlooking the pretty garden, which was the hobby of the most remarkable and resourceful secret agent in all Europe.