"Exactly," rejoined Uncle Brian drily. "When you are clear of Rioguay. But what chance would you stand to get even as far as Valodar without being arrested? My boy, you underrate the secret service of the republic. You might---I say might with great emphasis--you might gain possession of one of the flying-boats. But to what purpose? They'd fix your position with their magneto detectors. There would be half a dozen aircraft waiting for you before you as much as caught a glimpse of the sea. Even supposing you got as far as the supposedly neutral republics of San Benito or San Valodar, you'd find both places swarming with Rioguayan agents who wouldn't hesitate to stick a knife into your back, or pump half a dozen shots out of an automatic into you. Assassination under the guise of robbery. That's what would happen. No, Peter, it can't be done. We'll have to think of another way." "Have you thought of anything?" asked Peter, who for the first time fully appreciated the intricacies of the problem by which Uncle Brian was confronted. "I have," replied Uncle Brian. "I've been thinking it out for months--almost as soon as I discovered what I was engaged for. There's one line of retreat." He pointed to the chart, indicating a vast extent of mountainous country, through which several rivers wended their way. The whole district, judging from the map, was devoid of towns and villages. Occasionally an outpost was indicated, where detachments of armed police were stationed for no other apparent purpose than to keep watch over an uninhabited district. "Of course, we may not find these police posts," continued Uncle Brian. "Since the settlement of the boundary dispute they may have been withdrawn. Tajeco, whence our pipe line runs, is the only place of any consequence. Apart from that, the whole country is mountainous, with the valleys stiff with tropical forests. Now, this is my plan: see these two rivers--the Rio Tinto and the Rio del Morte? They both join the Rio Guaya at about thirty miles above Tepecicoa. As you know, ordinary navigation is impossible ten miles above the town, owing to shallows, but canoes and light draft craft can ascend both the Rio Tinto and the Rio del Morte for a considerable distance. In fact, the Rio del Morte has never been explored to its source, so the map is merely guesswork as far as that river is concerned. That's our way to freedom, Peter. It will be a difficult, a hazardous way, but with luck we'll win through." "We'll have a jolly good shot at it," declared Peter with grim determination. "But how can we get away from here without arousing suspicion? For anything we know, your friend Diaz may be keeping an eye on us already."