He worked his way down again, almost deafened by the noise of the fall. He came to where the water shot out of the mountain in a great arch. He wriggled his way towards it, and found a rocky ledge, wide and damp, just by the fall itself.

Mafumu stood and shivered with fright, for the noise was tremendous. It flowed all around him like rumbling thunder. He edged his way behind the great arch of water, for the rocky ledge stretched all the way behind.

And there, hidden in the misty spray that hung always around and about the waterfall, Mafumu thought that he had discovered another way into the Secret Mountain! For surely, where the water was able to come out of the mountain, he and Jack would be able to go in!

The moon was now almost gone, and darkness crept across the country. Mafumu shivered. He had a curious charm round his neck, made of crocodile’s teeth, and he took it into his hand to bring him good luck. He slid quickly down the mountain-side, grazing himself as he went, and bruising his ankle-bones as he knocked them against rocks and stones. But he did not even feel the hurt, so anxious was he to get back to Jack, and tell him what he had found.

He reached Jack as the dawn was breaking. Jack was awake, and very puzzled because Mafumu was gone. The boy looked white and worried. He simply had no idea at all what would be the best thing to do. He had almost made up his mind that he must try to move the rock somehow and get into the mountain so as to be with the others.

But Mafumu had other plans. In funny, broken English he tried to explain to Jack what his idea was.

“Big, big water,” he said, and made a noise like the splashing of the waterfall. “Jack come with Mafumu see big, big water. We go into big water. Come.”

Jack thought Mafumu was quite mad, but the other boy was so much in earnest that he nodded his head and said Yes, he would come.

Leaving their packs where they were, covered by boulders and stones, the two boys made their way back to the great waterfall. The noise was so deafening that they had to shout to one another to make themselves heard.

Mafumu remembered the way he had taken in the moonlight. He never forgot any path he had once travelled. He even remembered the bushes and rocks he had passed. So now he found it easy to help Jack up the rocky ledges to where the water gushed out of the mountain-side.

Jack was wet through and almost deaf by the time he reached the place where the water appeared from the mountain. He kept shaking his head to get the noise of the fall out of it — but it was impossible! It went on all the time.

Mafumu was excited. He led Jack behind the great curve of the fall, and showed him how the water thundered out just above their heads. It was a queer feeling to stand immediately under a great waterfall, and see it pouring down overhead and in front, a great blue-green mass of water, powerful enough to sweep the boys off and away if it could have reached them!

“How queer to stand behind a waterfall like this,” said Jack. “Mafumu — what’s the sense of bringing me here? How do you suppose we’re going to crawl through water that’s coming out of the mountain at about sixty miles an hour. You must be mad.”

But Mafumu was not mad. He took Jack right to the other side of the ledge, and pointed to a narrow rocky path that led into the mountain, where the water ran only two or three inches deep. Nearby, the river had worn a deep channel for itself — but this ledge was just above the level of the river, and had water on it only because of the continual splashing and spray that came from the fall.

“We go in here,” grinned Mafumu. “We go in here, yes?”

“Golly, Mafumu — I believe you are right!” said Jack, excited. “I believe we can go in here! Though goodness knows how far we’ll get, or where it will take us.”

“We go now,” said Mafumu. “Hurryup, hurryup.”

The boys squeezed themselves on to the rocky ledge. If they had slipped into the great torrent of water that poured out, that would have been the end of them. But they were careful to hold on to bits of jutting-out rock, so as not to fall. The ledge was damp and slippery. The air was full of fine spray. It was queer to be squeezing by a great river that became a waterfall two or three feet away from them!

The rocky ledge ran right into the mountain, keeping a foot or two above the level of the deep hidden river. The boys made their way along it. Soon they had left behind the thunder of the waterfall, and the mountain seemed strangely silent. Just below them, to their left, ran the underground river, silent and swift.

“It’s dark, Mafumu,” said Jack, shivering. It was not only dark, but cold. No sunshine ever came up the secret river! But soon a queer light showed from the roof and walls of the river tunnel.

It shone green and blue. Mafumu thought it was very odd, but Jack knew that it was only the strange light called phosphorescence. He was glad of its pale gleam, for now they could see more or less where they were going.

We shan’t fall down into the river now and be swept out into the waterfall,” he thought. “My goodness, Mafumu was clever to think there might be a way into the mountain, where the river came out and made a fall! I should never have thought of that in a hundred years! Wouldn’t it be marvellous if we could rescue everyone!”

After a long crawl along the ledge the tunnel opened out into a series of caves, some large, some small. The boys marvelled at some of them, for the walls were agleam with queer bright stones. Mafumu did not like them.

“The walls have eyes that look at Mafumu,” he whispered to Jack. Jack laughed — but he soon stopped, for his laugh echoed round and round the caves, and rumbled into the heart of the mountain and came back to him like a hundred giant-laughs, very queer and horrible.

On through the river-caves went the two boys, silent and rather frightened now. Then they came to what seemed a complete stop

“Mafumu! The river is in a tunnel here, and the roof almost touches the top of the water!” said Jack in dismay, “We can’t get any further.”

Mafumu waded into the river. It was not running very swiftly just there, for it was almost on the level. It was deep, however, and the boy had to swim. He began to make his way up the tunnel to see how far he could go with his head above the water. His head knocked against the roof as he swam — and presently he found that the water touched the roof! So he had to swim under the water, and hoped that before he choked the roof would rise a little and give him air to breathe!

Mafumu was a good swimmer, and was able to hold his breath well — but his lungs were almost bursting by the time that he was able to find a place to stick up his head above the water and breathe again. Even so, the roof fell low again almost at once, and the water bobbed against it. How far would it be before it rose again and Mafumu could breathe?

He had to try. There was nothing else to do, unless he and Jack were to go right back. So he took an enormous breath, dived down and swam vigorously below the water, trying the roof with his hand every now and again to see if he could come above the water and breathe.

He was rewarded. The roof suddenly rose up and the tunnel became a large cave! Mafumu waded out of the water gasping and panting, delighted that he had not given up too soon!

He sat down for a few minutes to get all the breath he could. He had to go back and bring Jack through now! He did not know if the other boy could swim under water as well as he, Mafumu, could!

Back went Mafumu, knowing exactly where to rise and breathe, and where to dive under and swim back to where Jack was anxiously awaiting him, wondering what in the wide world had happened!

Mafumu tried to explain to Jack what he was to do. Jack understood only too well!