"Hulloa! Why, here's a tunnel!" exclaimed Kennedy in surprise. "They've been down there, evidently! I wonder where it leads to?" Then, as they both glanced around, they saw a thin, twisted electric cable containing two wires which led from a cigar-box on the ground in a corner away down into the tunnel. Kennedy lifted the lid of the box, and within found an electric tapping-key with ebonite base and two small dry cells for the supply of the current. "Now what can this mean, I wonder? Some devil's work here, without a doubt!" he said. "Let us ascertain." Together the pair carefully descended into the narrow tunnel that had been driven into the side of the hill, evidently by expert hands, for its roof had been shored up along the whole length with trees cut from the wood. Away along the narrow passage they groped, finding it so low that they were compelled to bend and creep forward in uncomfortable positions until they came to a sudden turn. Whoever had constructed it had also succeeded--as was afterwards found-- in cleverly disguising the great heap of earth excavated. He had also probably misread his bearings, for at one point the subterranean gallery went away at right angles for about fifty yards, until there--where the atmosphere was heavy and oppressive because of lack of ventilation-- stood several petrol-tins. To one of them the end of the cable leading from the unsuspicious cow-shed had been attached. As they stood staring at the petrol-tins a sudden roar slowly approaching sounded directly overhead--a heavy rumble of wheels. Then it died away again. "Hark!" gasped Ella. "Isn't that a train? Why, we are directly under the railway-line running through the tunnel." "Yes, dear. A touch upon that key up in the shed and we should be blown out of recognition, and the tunnel, one of the most important on the line of railway communication running east and west across England, would be blocked for months." "That is what those devils intend!" Ella declared. "How can we frustrate them?" Seymour Kennedy reflected for a few seconds, holding his torch so that its rays fell upon those innocent-looking petrol-tins at the end of the cunningly contrived sap. Then he took up one of them and carrying it said: "Let's get back, dear. We know the truth now." "It is evident that they intend to blow in the tunnel from below," declared Ella, as they crept back along the narrow gallery. "Without a doubt," was her lover's reply. "Mr Horton, as he is known, took the house with but one object--namely, to cut the railway-line to the coast--the line over which so much war material for the front goes nightly. Truly, the Hun leaves nothing to chance." "And my father is actually assisting in this dastardly work?" "I'm afraid he is, darling. But so long as we remain wary and watchful, I hope we may be able to combat the evil activities of these assassins."