"Ah!" I said; "that's what we have to find out. And we shall do so before very long, if we are careful and vigilant." "Trust me," she said; "I am entirely at your orders." "Then I shall wait and hear your report," I said. "When you return to the hotel send a line to my room." And with that arrangement we parted. That day I spent idling in the vicinity of the hotel. It was mid-August, and the atmosphere was stifling. That district of Hull is not a very pleasant one, for it is one of mean provincial streets and of the noise of railway lorries rumbling over the granite setts. The afternoon I spent in playing billiards with the marker, when about six o'clock a page-boy brought me a note from my enthusiastic little friend. "I shall be in the station refreshment-room at half-past six. Meet me.--VERA." Those were the words I found within the envelope. Half an hour later, when I sat at the little marble-topped table with her, she related how she had been following the pair all day. "They were in the factory from half-past one until four," she said. "They've ordered a builder to put up ladders to examine the chimney. They appear to think it isn't quite safe." She told me the name of the builder, adding that the contract was to have the ladders in position during the next three days. "They are leaving for London to-night by the last train," she added. "I heard the Belgian telling the hall-porter as I came out." "Then we'll wire to Ray to meet them, and keep an eye upon them," I said. "I suppose you will go up to town?" "I think so. And when they return I will follow them down if Ray deems it best," replied the pretty girl, who was just as enthusiastic in her patriotism as ourselves. So still mystified I was compelled to remain inactive in Hull, while Vera and the two foreigners whom we suspected of espionage went up to London. For the next four days I heard nothing until suddenly, at eight o'clock one morning, Ray entered my bedroom before I was up. "I've found out one thing about those Johnnies!" he exclaimed. "They've been buying, in Clerkenwell, a whole lot of electrical appliances--coils of wire, insulators, and batteries. Some of it has been sent direct to the place they've taken here, and the rest has been sent to their house down in Sydenham." "What can they want that for?" I queried. "Don't know, my dear chap. Let's wait and see." "Perhaps, after all, they are about to set up in business," I said. "Neither of them has struck me as being spies. Save that they've visited Hartmann once or twice, their movements have not been very suspicious. Many foreigners are setting up factories in England, owing to the recent change in our patent laws." "I know," said my friend. "Yet their confidential negotiations with Hartmann have aroused my suspicions, and I feel confident we shall discover something interesting before long. They came back by the same train as I travelled."