Brat and Cowdie, at these words, peeped over the edge of the parapet, and saw, about a quarter of a mile away, a dense yellowish vapour coming slowly onward from a point where the enemy's lines curved round and faced the British lines from almost due south-east. The order was passed quickly down the lines for the men to don their gas-helmets, but the C.O. coming along the trench shortly afterwards, remarked that it could not possibly be gas, for, from the direction whence it came, it would pass onwards over a portion of the enemy's lines at a spot where the trenches curved back again and made a salient. At this point the lines twisted and bent themselves into many curious salients, for the last advance had not thoroughly straightened out the position. "The Germans are not such fools as to gas their own men, Grenfell, what do you say?" remarked the officer commanding the trench to Grenfell, who had come out of his dug-out to get a view of the cloud. "No, sir. There must be some other reason." "Yes, and the reason is, I think, a change of wind which is bringing on a dense fog." "You are quite right, sir," added the other, after regarding the air and sky for some ten seconds. "There has been a sudden change of wind, and a dense local fog is coming up from the valley. The whole landscape will be blotted out in a few minutes." "You're right, Grenfell," replied the officer. Then, turning to his orderly-sergeant, he called out: "Pass the order for the men to stand-to! There is no telling but that the Boches may come over the top with the fog, and try to surprise us." "Yes, sir," came the reply smartly, and the sergeant, saluting, disappeared along the trench, calling out the men from the dug-outs, and ordering a general "stand-to." The chance was too good to be lost. Cowdie gave Brat a dig in the ribs, and whispered to him, "Now is the time. See, the fog thickens, and it is nearly up to the wrecked aeroplane. Let's go over, or the Boches will be there first. They're sure to try it on. What say you?" "I'm with you, old man, but it will be an awful job. Have you got your revolver loaded, for we've got nothing else?" "Yes," replied his chum, feeling that his weapon was safe in the leather case, which hung at his left side. "Come on, then; we haven't a second to lose." The next instant they were over the top, and making a dash for the spot already hidden in the fog. "Come back there, you fellows!" cried a sergeant of the Wiltshires, whose company lined the trench. "Where the deuce are you going to?" "To save Lieutenant Dastral and his observer, sergeant! Don't let your men fire on us. We'll be back in five minutes," shouted Bratby. "Devil a bit of use you fellows throwing your lives away like that. The Boches are sure to attack under cover of the fog. Come back, the pilot must have been dead an hour. The machine was ablaze when it crashed," called the sergeant again.