Greene had cut out his engine; there was too much danger of an explosion, with the leaking petrol, to allow the spark to continue. He had to volplane down this time, not as a quick way of descending, but as the only means of preventing a disastrous fall. Even in broad daylight there is always risk in landing with a dead motor. Here, in the darkness and with unknown country below, the risk was multiplied a hundred times. All that Greene knew with any certainty was that he was over country broken up into fields. The fences were numerous, there were ditches, too, and obstructions of all sorts. The larger ones he could see readily enough, when he got close; it was the smaller ones that threatened the real danger. But if the danger was great, Greene was a master of his craft. He swooped downward. Then, when he was scarcely a hundred feet up, he caught the machine with a fine show of skill and held it, for a moment, on an even keel. "We'll chance it in the next field," he called. "Can't stay up any further. Here goes!" Down, down, they went. Then they were down, bumping along. But the element of luck that, despite all his skill, Greene had to have, favored him. The field was smooth and the monoplane came to rest safely. In an instant both were out, Greene first, since Frank, having to free himself from his straps, was delayed. "Quick! The small flashlight!" called the flyer. "Here, give it to me! If we're to save any essence we've got to be quick!" He took the light. But a quick look over the tank failed to show a spurting stream of gasoline. "By Jove! Wonder if I could have been mistaken? Perhaps it was something else they hit!" cried Greene. But then he groaned. As he unscrewed the cap of the tank and peered in, he saw that it was bone dry. CHAPTER XIII A DANGEROUS ERRAND 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."