"With submarines!" he exclaimed in obvious surprise. "Why, we have in hand at this moment several submarine inventions, of which we own the patents. Two of them are completely secret, and they are in use only by France and Britain." This put a new aspect on the affair. "I begin to see now," I said, "why your name has been assumed. Have you heard of any attempt to secure the submarine secrets?" "None whatever," replied Mr Engstrom. "Moreover, it would be extremely difficult, if not impossible. One of the appliances with which we are concerned is of such importance that, while we make the greater part of it, a vital portion is manufactured in England, and the apparatus is not put together until the whole is actually on the submarine for which it is intended. Consequently, unless a thief or spy secured copies of the plans both here and in England he would be powerless to profit by either. I may mention that this arrangement was arrived at with the British Admiralty at our express wish and suggestion. I am quite frank with you, Mr Sant." "One more question, Mr Engstrom," I added. "You are in a position to know of any important inventions in connection with submarine work. Have you heard of any recent invention which would bring it within the bounds of possibility that your double is acting honestly and has really something to sell?" "That is out of the question," returned the engineer decidedly. "Unless the invention were German, in which case it would not come out of that country, I think I should certainly have heard something of it. Of course, we have rivals in our business, but there is a certain amount of freemasonry even among business rivals. I know all the people who are making submarine parts--there are very few who could or would tackle a big invention. Besides, if the man has an honest bargain to drive, why should he assume my name?" This argument was unanswerable. But I confess I was still a long way from guessing just what the bogus Engstrom and his friends were plotting. My next visit was to the Swedish police in search of information about Madame Bohman. Here, however, I was quite at fault. It was evident she was passing under an assumed name, and I could not succeed in identifying her among the long array of photographs of known German agents laid before me by the chief of the Swedish Secret Police. Arriving at Bergen, I received, before I sailed for England, a long telegram from Madame Gabrielle, telling me that Engstrom, Madame Bohman, and Thornton had left for Paris. Fearing that they would immediately recognise her if she followed them, she had telephoned the news to Hecq, and that astute official had promised to take the suspects under his own wing for the immediate future, pending my arrival. I proceeded to London, where, to my dismay, I learned that, although Madame Bohman had arrived in Paris with Thornton, Engstrom was missing.