As the boys crept down the rocky passage, they suddenly heard a curious noise in the distance. They stopped.

“What’s that noise?” asked Jack. It was a kind of rumbling, gurgling sound, sometimes loud and sometimes soft. The boys listened.

“I don’t know,” said Mike, at last. “Come on. Maybe we shall find out.”

On they went again, and very soon they discovered what the queer noise was. It was made by water! It was a waterfall in the mountain, a thing the children had not even thought of! They came out into a big cave, and at one end fell a great stream of water. The cave was damp and cold, and the boys shivered.

They went over to the curious waterfall. “I suppose the snow melts on the top of the mountain and the water finds its way down here,” said Jack, thoughtfully. “It must run through a rocky passage, something like the one we have just been in, and then, when the passage ends, the water tumbles down with that rumbling noise. I’m quite wet with the spray!”

The water fell steadily from a hole in the roof of the cave, where, as Jack said, there must be a tunnel or passage down which the water ran before it fell into the cave.

“Where does the water go to, I wonder?” said Mike. “It rushes off into that tunnel, look — and becomes a kind of river going through the mountain. I think it’s weird. I wonder if the robbers live in this cave — but there still seems to be no sign of them or their belongings. After all, if people live somewhere, even in a cave, they scatter a few belongings about!”

But there was nothing at all to be seen, and, as far as the boys could see, no way of getting out of the “waterfall cave,” as they called it.

They wandered round, looking for some outlet — but the water seemed to have found the only outlet — the tunnel down which it rushed after falling on to the channelled floor of the cave.

The boys went back to the water and gazed at it. Jack saw that through hundreds of years the waterfall had worn itself a bed or channel on the floor of the cave, and that only the surface water overflowed on to the ground where the boys stood. The channel took the main water, and it rushed off down a tunnel, and then was lost to sight in the darkness.

“I suppose the robbers couldn’t possibly have gone down that tunnel, could they?” said Paul suddenly. “There isn’t a ledge or anything they could walk on, is there, going beside that heaving water?”

The boys tried to see through the spray that was flung up by the falling water. Jack gave a shout.

“Yes — there is a ledge, and I believe we could get on to it. For goodness’ sake be careful not to fall into that churning water! We’d be carried away and drowned if so, it’s going at such a pace!”

The boy bent down, ran through the flying spray, and leapt on to a wet ledge beside the water, just inside the tunnel into which it disappeared. He nearly slipped and fell, but managed to right himself.

He flashed his torch into the tunnel and saw the amazing sight of the heaving, rushing water tearing away down the dark vault of the mountain tunnel. It was very weird, and the noise inside the tunnel was frightening.

Paul and Mike were soon beside Jack. He shouted into their ears. “We’d better go along here and see if it leads anywhere. I think this is the way the robbers must have gone with Ranni and Pilescu. Keep as far from the water as you can and don’t slip, whatever you do!”

The boys made their way with difficulty along the water-splashed tunnel. The water roared beside them in its hollowed-out channel. The noise was thunderous. Their feet were soon wet with the splashing of the strange river.

“The tunnel is widening out here,” shouted back Jack, after about an hour. “Our ledge is becoming almost a platform!”

So it was. After another minute or two the boys found themselves standing on such a broad ledge that when they crouched against the back of it, the spray from the river no longer reached them.

They rested there for a while. Paul was terribly tired by now. Mike looked at his watch. It was four o’clock in the morning! The sun would be up outside the mountain — but here it was as dark as night.

“I feel so sleepy,” said Paul, cuddling up against Mike. “I think we ought to have a good long rest.”

Jack got up and looked around the broad platform for a more comfortable resting-place. He gave a shout that quickly brought the others to him.

“Look,” said Jack, shining his torch on to a recess in the wall of the tunnel at the back of the platform. “This is where the robbers must sometimes rest before going on to wherever they live!”

In the recess, which was like a broad shelf of rock, lay some fur rugs. The boys cuddled into them, snuggled up to one another, closed their eyes and fell asleep at once. They were tired out with their night’s travel.

They slept for some hours, and then Jack awoke with a start. He opened his eyes and remembered at once where he was — on the inside of the mountain! He sat up — and suddenly saw the platform outside the recess where the boys were, was lighted brightly. Voices came to him — and he saw a flaring torch held high. What could be happening now?

The other boys did not wake. They were too tired to hear a sound! Jack leaned out of the rugs and tried to see who was holding the torch. He had a nasty shock — for it was held by one of the robbers! When Jack saw him turn round and his red wolf-tail swing out behind him, he knew without a doubt that the robbers were there within a few feet of him.

The boy tried to see what they were doing. They were at the edge of the river, at the end of the rocky platform. As Jack watched he saw two more men come up from the ledge that ran beside the river. It was plain that the broad platform they were on narrowed into the same sort of ledge that ran beside the upper part of the river. The men were coming up from lower down — and they were dragging something behind them, something that floated on the water. Jack could not see what it was, for the light from the torch flickered and shook, making shadows dance over everything.

The men called to one another hoarsely. They did something at the edge of the water, and then, without a glance toward the recess in which the boys were sleeping, they turned and made their way up the tunnel through which the boys had come, keeping along the ledge in single file. They were going up to the temple-cave, Jack was sure.

“Going to rob people again, I suppose!” thought the boy, excitedly. “They’ve taken Ranni and Pilescu somewhere further down, and tied them up, I expect — left them safe, as they thought. Golly, if only we could find out where they are, we could rescue them easily now that the robbers have left them for a while.”

He looked at his watch. It showed ten minutes to nine! It was morning. Would Yamen and Tooku, Beowald and the villagers have arrived at the temple-cave yet, and meet the robbers on their way? Jack could not imagine what would happen. He woke the others and told them what he had seen.

“The thing to do now is to get along as quickly as we can, and find out where Ranni and Pilescu are,” he said. “The robbers have gone in the opposite direction. Come on, I saw where they came from. It’s plain they follow the river.”

The boys shook off the warm rugs. Jack flashed his torch round the comfortable recess to make sure they had left nothing behind. The light fell on a tiny shelf at the back. In it was something wrapped in a cloth. Jack unwrapped it in curiosity. Inside was a big Baronian loaf, crusty and stale.

“We’d better soak it in water and eat some,” said Jack, pleased. “I’m hungry enough to enjoy bread and water, even if you two aren’t! I suppose the robbers leave bread here to help themselves to when they rest in these rugs.”

When they pulled off the crust of the big loaf they found that the bread was not too hard to eat after all. They did not even need to soak it in water. Paul, as usual, had a big packet of the honey-flavoured Baronian chocolate with him, and the three boys thoroughly enjoyed their strange meal beside the rushing mountain river.

There was a flattish sort of cup on the little shelf where they had found the bread, and the boys dipped this into the clear river water and drank. It was as cold as ice, and tasted delicious.

Jack bent down to fill the cup again and something caught his eye, as he flashed his torch round. He stopped and gave a surprised exclamation.

“Whatever’s that? Look — that thing over there?”

The others looked. Tied by a leather thong to a jutting rock was what looked like a hollowed-out raft. It was broad and flat, with a hollow in the middle. The sides were strengthened with strip upon strip of leather, bound tightly over the edges.

“It’s a raft-boat, or boat-raft, whatever you like to call it!” said Mike, surprised. “I’ve never seen anything like it before. Isn’t it odd? What’s it for?”

“To go down the river, I imagine!” said Jack, joyfully. “My word, we shall soon get along if we use that raft!”

“But how did the men get here on it?” said Paul, puzzled. “They couldn’t float against the current, and it’s very strong here.”

“They probably crept up on the narrow rocky ledge that seems to run beside the river all the way,” said Jack. “But behind them each time they come, they must drag a raft like this, which they use to get themselves back quickly. I say, this is getting awfully exciting! We can take the raft for ourselves, and that will mean that we leave the robbers I saw just now far behind us, for they will have to walk along the ledge as we did, instead of using their boat. Come on — let’s try it!”

“I shouldn’t be surprised if it takes us right to the place where Ranni and Pilescu are prisoners,” said Paul. “Undo that leather thong, Mike, and let’s get into the funny boat.”

The boys untied the leather strip, and got into the hollow centre of the solid raft. It was absolutely unsinkable, made out of wood from a big tree, hollowed out carefully in the middle. The boys soon found out why the edges were bound so thickly and firmly with strips of leather!

They let the raft go free on the rushing stream. At once they floated into the dark tunnel from which Jack had seen the robbers come. The raft swung round and round as it went, and bumped hard against the rocky sides of the strange dark tunnel. The leather edges took off the worst jolts, but even so, the boys had to cling tightly to the raft to prevent themselves from being jerked overboard!

“This is the most exciting thing we’ve ever done!” shouted Jack, above the roar of the water. “Golly, aren’t we going fast! I hope we don’t come to a waterfall!”

Down they went on the rushing mountain river, down and down in the darkness. The raft rushed along as fast as a speed boat, and the three boys gasped for breath. Where did the river flow to?