The exploration of the side passage leading off from the tunnel amounted to little. Corporal White said he saw no trace of the four men, but he reported that there was a maze of passages leading from the one he examined, and it was possible for the four to have hidden in these, or to have made their escape along one of the dark, winding tubes of earth. "Well, this makes the mystery all the more puzzling," said Jimmy, when he and his chums talked it over. "I certainly would like to know who those fellows were--especially the ones in uniform." And there was a deeper mystery about it than he even dreamed of. But little the worse from their nerve-racking experience in the collapsed dugout, Jimmy and his chums finished their period of leave and once more took their places with their comrades, ready to fight or do anything else required of them. Iggy was given a detail as orderly to a major, which made his duties light. But he was anxious to get on the firing line again. It was early one morning--quite a zero hour, in fact, though none was set--when suddenly there began a furious firing from the German lines, removed only a short distance at this particular part of the front where the Khaki Boys were stationed. If the German gunners hoped to take the Americans by surprise, and by a sudden and unexpected barrage pave the way for an attack, they must have been sorely disappointed. For almost at the very instant that the German pieces began their grim music there was response from Uncle Sam, and in greater volume. But it was not to be altogether an artillery duel. The word was passed up and down the line to get ready to repel an attack in force, and Jimmy, Roger, Bob, and Franz tumbled out of their blankets, their eyes heavy with sleep, ready for the fight. It was not long in coming, for no sooner did they have their equipment on, from gas masks at the alert position to their canteens and mess kits, than they were ordered over the top. "Forward! Forward!" was the cry. The American fire, at first a mere reply to the challenge of the Boche artillery, was soon changed into a protecting barrage for the thousands of doughboys who scrambled out of their trenches, and in less time than would seem possible a fierce battle was raging. Jimmy had one glimpse of Bob, Roger, and Franz being directed off to the right, while his party was ordered to the left. So, for the time, Jimmy lost sight of his chums. The battle was fierce and hot. In spite of the American barrage, the Germans broke through at one point, and there was hand-to-hand fighting, grim and terrible while it lasted. Jimmy Blaise was in the thick of this. He had one vision of a big burly German charging him, his mouth wide open in a yell, and his bayonet dripping red. Then Jimmy's rifle spoke, and the German was no longer in front of the Khaki Boy, who leaped over his body to keep beside his comrades.