The big chemical laboratory, which her father had established in secret in that long attic, presented the same scene as it had when he had visited it before at the invitation of his well-beloved. With such constant demands upon his inventive powers, it was necessary that the Prussian ex-professor should have the place fitted up with all the latest scientific appliances. "Well, Seymour!" the girl exclaimed at last. "Here you are! What do you think of these?" And, crossing to a side table, she indicated two well-worn attache-cases in brown leather, each about sixteen inches by eight, and three inches deep. One of them she opened, revealing a curious mechanism within, part of which was the movement of a cheap American clock. Her tall, good-looking companion, who was a skilled mechanic, examined both these innocent-looking little cases with keen interest, and then exclaimed: "Ah! I quite understand now! These are no doubt to be used in conjunction with explosives. They run for half an hour only, and then electrical contact is made into the explosive compound." "Exactly. See there, that row of tins of lubricating-oil. They are already filled with the high-explosive and in readiness." Kennedy bent and then saw, ranged below a bench on the opposite side of the laboratory, six tins of a certain well-known thick lubricating-oil used by motorists. "There is sufficient there, dear, to blow up the whole of Barnes," she declared. "Evidently this latest outrage is intended to be a serious one." "Ah!" sighed Kennedy. "It is a thousand pities, Ella, that your father is doing all this dastardly secret work for the enemy. Happily you, though his daughter, are taking measures to thwart his plans." "I am doing only what is my duty, dear," replied the girl in the kimono; "and with your aid I hope to upset this latest plot of Ortmann and his friends." "Have you seen Ortmann lately?" her lover asked. "No. He has been away somewhere in Holland--conferring with the German Secret Service, without a doubt. I heard father say yesterday, however, that he had returned to Park Lane." "Returned, in order to distribute more German money, I suppose?" "Probably. He must have spent many hundreds of thousands of pounds in the German cause both before the war and after it," replied the girl. The pair stood in the laboratory for some time examining some of the apparatus which old Drost, now sleeping below, had during that day been using for the manufacture of the explosive contained in those innocent-looking oil-cans. Kennedy realised, by the delicacy of the apparatus, how well versed the grey-haired old Prussian was in explosives, and on again examining the attache-cases with their mechanical contents, saw the cleverness with which the plot, whatever its object, had been conceived. What was intended? There was no doubt a conspiracy afoot to destroy some public building, or perhaps an important bridge or railway junction.