For a moment Greene was speechless with despair. Fate had tricked him, it seemed, after he had done his best—and a better best than most men could even have attempted. Then he grinned.

"We'll have to hoof it," he said. "A good twelve miles, too! If we were champions at cross-country work it would take us the best part of two hours. And it's so long since I've used my legs that I don't know how long I'll be."

"There's one chance," said Frank. "I remember that I saw a little inn on the road the Germans took this afternoon. We're not so very far from that now. These little inns along the roads in France all have petrol for motorists who run short. If I went there I might get some."

Greene shook his head doubtfully.

"The government's taken all the essence it could find," he said, "I don't believe they'd have any. And, besides, there's a good chance that the Germans have men there."

"Still it's a chance," said Frank. "Won't you let me try? If I can't get it we shan't lose much time. And if I do, look at the difference it would make."

"That's true enough," said Greene. "All right, try it. I'll mend up the hole, when I find it, and if you do get some essence, we can be off at once. Good luck!"

Frank was on his way already, slipping away in the direction whence they had come. Luckily enough, he got his bearings by the windmill from which he had observed the wood into which the Germans had gone. To make his way to the road along which he and Henri had first seen the Germans passing was an easy matter. But he was afraid of roads by this time, and the more so because he knew that the Germans, having been aroused by the attack from the sky, would be doubly on the alert. So he stuck to the side of the road, religiously taking advantage of every bit of cover he could find to escape the foe.

"They knew they'd given themselves away just as soon as they fired at us," he reasoned, thinking half aloud as he trudged along, which was a habit of his. "And I don't believe they know they hit us at all. They do know that they didn't bring us down at once. Anyhow, there's no reason for them to be secret any more, and if they stay in that wood, they'll throw out pickets now, because they'll think that as soon as we went back and made our report troops would be sent to rout them out. It's up to me to be mighty careful."

That was good sound reasoning, too. From all he had learned since the war began, he knew that the Germans were by no means foes to be despised. They had been pretty generally victorious, but that was not all. They had shown a capacity for being always ready, for thinking of everything that might come up to block their plans. And he was sure, therefore, that the German commander would not argue that the aeroplane had got clean away just because the probabilities indicated that it had. He was almost certain to beat the country within a reasonable area for it, in the hope of finding it crippled and thus unable to carry the news it had come to get.

"I bet the Germans wouldn't have sent just one aeroplane," he reflected. "They'd have sent two, so that if anything happened to one, the other could have brought back the news."

But though he was thinking hard, he didn't linger as he went. Soon he came to the transverse road along which the Germans had gone, and turned in the direction they had taken. It was beginning to rain a little now, and it was very dark. He still stuck to the fields, though he was close to the road, and he found nothing to bar his way to the inn. When he got there, moreover, he found the place dark and deserted. Not a soul was in sight, but there were evidences that spoke as eloquently as men or women could have done. In the tap room furniture was smashed and broken and shattered glass was about the floor. Plainly the Germans had stopped as they went by.

"Of course!" he said, to himself. "If there were people here they took them along with them. They wouldn't be likely to leave any French people, whose first idea would be to tell what they had seen! It's certainly lucky that they didn't see us. We'd be with them now, I guess."

It was spooky work exploring the abandoned inn in the damp, dark night and with the knowledge that German soldiers were probably no great distance away. It was less than a quarter of a mile to the edge of the wood that had assumed such an important aspect, and he expected at any moment to hear the footsteps of intruders. None the less he went about his task quietly and coolly.

"If they had any essence, they'd hide it," he said to himself. "They'd know that both armies would need it for automobiles and aeroplanes, and they'd try to keep any they had left. So it won't be in any of the usual places."

For that reason he did not even leave the main building to make a search in the stable that was used as a garage. Instead, he went into the cellar. Here it was still plainer that the Germans had passed through. His feet stepped into puddles of sticky dampness, and, using his flashlight, he saw that it was wine. The heads of casks had been knocked in; broken bottles, too, strewed the floor.

This, however, had not been wanton destruction, he was sure. It had an object, and that object had been to prevent the soldiers from getting anything to drink. Troops on an errand requiring such extraordinary secrecy as had been maintained in this case could not be allowed to drink any liquor. That would have spoiled in all likelihood the remarkable discipline of which Captain Greene had spoken.

But, once more, it was not his business to think of what he saw, or to speculate about it, but to find the petrol if any was to be found. And he stumbled upon the hidden store quite suddenly, and quite literally, too. In one corner of the cellar was what looked like a pile of kindling wood. Harry kicked it indifferently in passing, and was almost thrown when his feet encountered a resistance more solid than he had any reason to expect. He looked down, and there, under the kindling, were two ten-gallon cans of petrol!

"I knew it must be there!" he cried to himself. He was down on his knees in a moment, shaking the cans to make sure that they were full. One had never been broached; the other was nearly half full. And this second can was the one he took. That would be more than enough to get the monoplane back to headquarters, and there was no reason for burdening himself with too great a load. He picked up the can, and at the same moment his heart leaped up into his throat, for overhead there came the sound of heavy footsteps. For a moment he stood as if paralyzed, listening.

The footsteps continued; guttural voices sounded,—the voices of Germans. It was impossible to distinguish what they were saying; and it made no difference, in any case. The only point that mattered was that they were there; that they blocked the only means Frank had of getting away with the precious petrol he had so luckily found.

He was safe enough personally. Even if they were led to come down into the cellar the chances were all in favor of his being able to conceal himself. What he feared was that some use was to be made of the place, and that the men whose voices he heard would stay there, thus preventing him from getting out of the building and so getting the petrol to Greene. It was more than possible, he thought, that the German commander, knowing that the presence of his troops in the woods had been discovered, would decide to use this place for headquarters.

And what he could hear confirmed this idea. There was a continual tramping overhead. Men came and went. That seemed to indicate that the occupation was to be permanent. He racked his brains for some means of escape. Windows there were none in the cellar. He found no trace of a trap door, such as there would have been in almost any American cellar. And then the saving thought came to him like a flash. He debated for a moment, then decided that the risk was worth taking. First he took his can of gasoline to the steps. Then he poured a little into a broken bottle, and poured this, in turn, on the wood under which he had found the cans. He dragged the full can of petrol to the other side of the cellar. And then, very deliberately, he set a match to the gasoline soaked wood and retreated to the steps.

The fire he had started blazed up at once, owing to the petrol. And at once a thick, acrid smoke filled the place. He was well up on the stairs, and thus safe from being choked. But he was in danger should the Germans come down, though even so, since the steps were wide, there was a chance for him. But he did not expect them to come down. He thought the smoke would drive them out, since as nearly as he could judge his fire was directly under the room in which the most of the commotion upstairs was taking place.

It was not long before he heard coughing upstairs, the first sign that the smoke was doing its work. By that time a brisk fire was burning. It had run up the posts to the beams that formed the chief support of the room above, and to his delight Frank saw that these burned far more fiercely and quickly than he had hoped. Plainly the wood was old and dry.

Above, as the fire spread, louder cries succeeded the coughing. And then came the crucial test by which his daring experiment had to stand or fall. Some one opened the door at the head of the stairs. Now, if ever, he was to be discovered! But as the door was opened the smoke was drawn up, and the German who had come to it jumped back.

"The whole place is burning! Get out!" he cried, in German. "There may be explosive spirits still down there!"

He slammed the door shut, and Frank heard running footsteps above. He waited until there were no more, and then, almost overcome by the smoke, slipped through the door. No one was left in the hallway into which he came. The place was full of smoke. He did not venture to the front door by which he had entered, but, still dragging his can of petrol, went to the back. Going through the kitchen, he found another door, as he had been sure he would and in a moment he was drinking in the cool, fresh air. The rain that was beating down on him now was welcome.

Just as he reached the open there was a sharp explosion behind him, and he looked back, to see the windows on the ground floor glowing. That was the other can of petrol, as he could guess readily enough. At once he ducked, and, running low, got well to one side of the house. Then, just as a great burst of flame lighted up the whole scene, he dropped to the ground, and lay peering toward the road in front of the inn.

A dozen officers and as many men, all in the German uniform, with the spiked helmets that made them so unmistakable, were in the road, staring at the burning house. And it was not until Frank saw how angry one of the officers was that he realized what a useful idea his had really been. Now detection of the Germans was certain. Investigation was almost certain to be made of a fire in a building so far out of the range of the German artillery as this. And so, even if neither he nor Captain Greene got back in time, the torch he had lighted, meaning only to secure his own escape, was likely to prove a death blow to the German hopes of secrecy.

Frank could not hear what the Germans were saying, but he had no intention of getting closer in an attempt to do so. Instead, having satisfied himself that there were no pickets behind the burning inn, he began crawling cautiously to the rear. It was a difficult task, especially so because of the petrol, which was no light burden. But he managed to get well out of the lighted zone and then he decided that it would be safe to straighten up and walk along.

As he went along the burning building served him well. It gave him a fixed landmark from which he could lay his course to the spot where he had left the monoplane and Captain Greene. By looking back from time to time he could correct his course, when he was crossing fields. And so without the guidance of roads, and partly to make better time and partly to avoid stray German pickets, he chose to stay away almost entirely from the roads and go across country.

From the fields in which they had descended to the inn the distance, as nearly as he had been able to guess it, was about a mile. He shortened this somewhat on the return trip. And he was within a quarter of a mile of the meeting place when he became suddenly conscious of something that was not just right. At first he was tempted to stop, but he overcame the temptation. The thing that had warned him of a possible danger was a trifling noise, yet one that was out of the ordinary. What the noise was he could scarcely have told. Perhaps the breaking of a twig, perhaps the slipping of a foot along a suddenly encountered patch of mud. At any rate he was sure that he had been followed.

He slowed down and now he could hear, or thought he could, the heavy breathing of at least two men. He was not certain of this; he was willing to admit to himself that he might be fancying it.

"If they're after me, why don't they take me?" he wondered to himself. But the explanation came to him almost as soon as he had asked himself the question. Whoever was following him could reason from the sight of the can of petrol he was carrying that he was going to some definite place where that petrol was wanted. And it would require no great stretch of the imagination for his trailers to decide that he must be carrying fuel to the aeroplane that had worked such havoc with the German plans.

"They think I'll lead them to the 'plane," he thought. Half a dozen plans for misleading them came to him. But none seemed practicable. Frank was intensely dogged in his determination to accomplish anything he had set out to do. The idea of giving up now, even to mislead his pursuers and so save Captain Greene from capture, was repugnant to him. He wanted to foil the men behind him—unless, as was possible, he only imagined that they were behind him—and still do what he had set out to do, which was in this instance to refill that empty petrol tank on the monoplane.

It was the purely accidental movement of putting his hand into his pocket to dry it off that gave him the idea. It met the pocket flashlight Captain Greene had given him, and at once he remembered a use for it of which the aviator had told him. To follow the plan did not mean that it would succeed, but it represented a chance, anyhow. And so when he came to the fence which he remembered climbing on his way from the monoplane, he stopped on the top rail, having pushed his can of petrol through first. In the field now immediately in front of him, but far away still, on the other side of the field, lay the monoplane. He could not see it in the driving rain but he knew that it was there.

There too would be Greene, waiting for him, and in all probability at this moment straining his eyes watching for his return. On that depended his chance of success in the plan that had come to him. On that, and on Greene's presence of mind and quick-wittedness.

So, still astride of the top rail, he began signalling with his pocket flashlight. He spelled out his message in Morse code, using a long pressure of the releasing switch for the dash and a short one for the dot. Word by word he spelled out his message, telling that he suspected that at least two Germans were trailing him. And at the end he signalled a request that if he had understood, Greene should wait a half minute and then imitate an owl's cry. He chose an owl because he had heard one or two earlier in the night. And he added that if he got the signal he would keep on heading for the monoplane. He suggested nothing to Greene; the rest was decidedly up to the aviator. Frank had done his share.

If there were Germans actually within sight of him, they did not attempt to interfere with him while he was flashing his message. But he had reckoned confidently that they would not. He was sure that he had not betrayed the fact that he knew he was being followed, and they would naturally suppose that this stop for signalling was part of a pre-arranged plan. He now dropped to the ground, picked up his can and took two or three quick steps. Then he stopped abruptly and was sure that he heard a footstep behind him. He grinned to himself, and just then the hoot of an owl sounded. Then he went on.

"I'll make it easier for them," he said. "Perhaps they wouldn't like to follow me right across the field!"

So he skirted the fence and the hedge at the side, and went around three sides of the field to reach the monoplane. And, as soon as it was in sight, all his suspicions were verified, for from behind there came a sharp exclamation in German, and he was told to stop, just as a heavy hand gripped his shoulder.

"Ja, we were right!" exclaimed one man in German. "There is their aeroplane! Now for the other—"

He never finished the sentence. Instead, he threw up his hands and pitched forward, just as a revolver cracked sharply in the silent night. With an oath the man who held Frank threw him aside, at the same moment shooting in the direction of the flash of Greene's pistol. But the Englishman's revolver spoke at the same moment, and he too fell. Frank's ruse had saved the day!