It was half-past eight in the morning before the voyage was resumed. Before long, the confluence of the Rio Tinto and the Rio del Morte was sighted. Brian, who was steering, ported helm and shaped a course towards the left bank, where the latter tributary joined its coffee-coloured waters with those of the Rio Guaya.
Presently Peter, who was engaged in cleaning out the barrel of his Express rifle, happened to glance skywards. Following the boat at a height of about two thousand feet was one of the units of the Rioguayan air fleet.
How long the flying-boat had had them under observation, neither Peter nor his uncle could say. The rapid throb of the outboard motor had prevented them hearing the deeper roar of the flying-boat's quadruple engines.
Knowing to an almost absolute certainty that the aircraft's crew had them under clear observation by means of powerful binoculars, Uncle Brian carefully avoided looking up. A sudden alteration of helm would be a false move. He kept steadily in his course for a few minutes before putting the helm to starboard and making for the Rio Tinto.
"That's awkward," remarked Uncle Brian. "They won't leave us alone. We'll have to make a feint of ascending the Rio Tinto. It will mean a day's delay and a night dash for the Rio del Morte."
"Perhaps when they see we're well on our way up the Rio Tinto they'll clear off," hazarded Peter.
Apparently his surmise was correct, for after circling overhead for three hours, the flying-boat disappeared in the direction of Tepecicoa, without having made any attempt to molest or even communicate with the Englishmen.
During the heat of the day the fugitives rested, anchoring their little craft by means of a big stone and a rope in the shade of an overhanging tree. Here they were screened from aerial observation, but no buzz of propellers disturbed their rest. The flying-boat had, in fact, returned to the base with the news that the mad Englishmen had really taken the Rio Tinto course.
It was not until four in the afternoon that the outboard motor was restarted and the course retraced to the Rio Guaya. Not without considerable trepidation, Brian steered across the broad river and made the narrow entrance to the sinister Rio del Morte.
Here the banks were lofty and precipitous, the stream flowing at the rate of four miles an hour through a bottle-necked gorge of less than a hundred yards in width and nearly a mile in length.