"You are at liberty to act as you please. You know their plans, and I have perfect confidence in you, Mackenzie," replied the officer. "Do not, however, mention a word of the enemy's intention to any one. It would terrify the men; and although I do not doubt their bravery, yet the knowledge of such a horrible fate hanging over them must necessarily increase their anxiety, and thus prevent them from doing their best. We are weak, but remember we are all Britons. Now come," he added, "sit there, upon that box, and explain at once what is your scheme of defence against this extraordinary attack." And the fearless man to whom the General had entrusted the defence of Edinburgh obeyed, and commenced to explain what means he intended to take--a desperate but well-devised plan, which drew forth words of the highest commendation from the commanding officer and those with him. They knew that the fate of Edinburgh hung in the balance, and that if the city were taken it would be the first step towards their downfall. CHAPTER XXXI. "THE DEMON OF WAR." Two hours later, just before the break of day, British bugles sounded, and the camp on the Braid Hills was immediately astir. That the enemy were about to test the efficiency of a new gigantic engine of war was unknown except to the officers and the brave man who had risked his life in order to obtain the secret of the foeman's plans. To him the British General was trusting, and as with knit brows and anxious face the grey-haired officer stood at the door of his tent gazing across the burn to Blackford Hill, he was wondering whether he had yet obtained his coign of vantage. From the case slung round his shoulder he drew his field glasses and turned them upon a clump of trees near the top of the hill, straining his eyes to discover any movement. On the crest of the hill two Volunteer artillery batteries were actively preparing for the coming fray, but as yet it was too dark to discern anything among the distant clump of trees; so, replacing his glasses, the commanding officer re-entered his tent and bent for a long time over the Ordnance Map under the glimmering, uncertain light of a guttering candle. Meanwhile the Russians were busily completing their arrangements for striking an appalling blow. Concealed by a line of trees and a number of farm buildings, the little section of the enemy had worked indefatigably for the past two hours, and now in the grey dawn the contents of the mysterious boxes, a long dark monster, lay upon the grass, moving restlessly, trying to free itself from its trammels. It was a huge and curiously-shaped air-ship, and was to be used for dropping great charges of mélinite and steel bombs filled with picric acid into the handsome historic city of Edinburgh! Some of the shells were filled with sulphurous acid, carbon dioxide, and other deadly compounds, the intent being to cause suffocation over wide areas by the volatilisation of liquid gases!