There was no sign of any one having been to the pond since the morning. Still, he could not be sure. He felt a strange feeling inside him, as he stood all alone on the bank and looked down into the water. The evening sun was shining full on it; he was glad; it would be easier to see when he was under. What would there be down there? He clenched his fists and said the Cub Promise between his teeth to buck him up. Then he suddenly remembered his dream and how brave he had felt when he was a Crusader-knight, about to challenge the lurking traitor in the Abbey. Before his courage had time to fail he dived, straight as an arrow, into the pond.

It was very different down there from what it was in the sea. All was a murky, brownish colour. Black, slimy weeds waved about, like wicked little clinging hands. He swam about gently but could see nothing unusual. Soon he had to come up for more air. Taking a very big breath, he dived again. This time he happened to be very near the side. In order to keep down and look well about him he caught hold of a big bunch of weed growing on the wall of the pond. Suddenly, just before him, he saw a black, cavernous hole in the bank. It was about three feet across and seemed like the entrance to a passage, leading away from the bottom of the pool. But it was full of water, of course.

Danny rose to the surface for breath, and ideas crowded into his mind. A passage leading away from the bottom of the pond! Then that was where the men went, and where the bicycle had disappeared to for which they had dragged the pond so carefully. But why did not all the water run away? Then he remembered that water never rises above its own level. On that side of the pond the bank rose steeply towards the high ground where the ruined mill stood. If the passage led up in a steep incline, or in steps, it would very soon be on a level with the surface of the pond. The water, flowing into the passage, would rise as high as this, and no higher. The level of the mill and the road was high enough for the passage to rise beyond the water altogether, and still be underground. Did it do this? The only way to find out was to dive again, swim into the passage, and see! He would have to take a very big breath to bring him up where the passage came up, and to let him get back if it did not seem to be rising. It was something of a risk. But Danny had nerved himself to anything. “If I do find a passage it will be jolly dark,” he said. And then he remembered that he had brought his pocket electric light, and had hidden it, with his handkerchief, knife, and two pennies, on the bank before diving. He would take his light down. Perhaps the water would not hurt the battery. Scrambling out on to the edge he soon found his torch, and stowed it away in the pocket of his shorts. Then, taking a mighty breath, he dived again, and swam straight into the dark passage.

Almost at once his outstretched hands came in contact with something hard and slippery. It was the bottom step of a flight of stone stairs. A moment later Danny was half swimming, half scrambling up them. His store of air was very nearly exhausted when, to his intense relief, his head suddenly came up above the water, and he breathed again. It was pitch dark, and he was standing in water up to his neck. He was safe from drowning, however—that was one thing to be thankful for! He had reached the top step of the flight, and was walking on a slippery surface that seemed to be inclined uphill, as he found that before long his shoulders were out of the water, and then he was only waist-deep. He took out his electric torch and pressed the button. To his joy he found the battery was working, and a ray of golden light shot through the darkness. Turning the light from side to side he saw that he was in a low, vaulted passage, walled and roofed with stone. There was nothing else to see. The passage seemed to go straight ahead. There was nothing for it but to go on, and hope there was no one else down there!

Danny had not walked many yards before his light glinted on something. Peering closer he saw that it was a bicycle leaning up against the wall. “So that’s where the bike went!” said Danny triumphantly, wishing the Kangaroos could see it, as he remembered their cutting remarks the day they dragged the pond in vain.

The bicycle was rusty and useless. The bareheaded stranger who had been in such a hurry that day on the road, and had said that he was going one way when he was really going another, must simply have been flying from his pursuers, and have thrown his stolen bicycle into the pond so as not to leave a clue when he dived down into his wonderful hiding-place!

So the mystery of the bicycle was solved at last! Danny had been determined to solve it. But in working at it he had come on still more mysterious things. It was a big affair this. And now he felt himself well on the way to clearing it up. Had he not got into the most secret hiding-place of the gang? With his heart beating fast with excitement he pressed on along the passage. He had reached dry ground at last. The air was musty and suffocating. Danny the Detective thought that this adventure would solve the whole problem; he little knew all that was to befall him and his country before the mystery would be finally brought to light.

His heart beating fast with excitement, Danny pressed forward through the damp darkness. There was a silent horror about this place. Mildew stood on the walls. Black creatures scurried away beneath his feet, afraid of the light. How often Danny had longed to find a secret passage! But now that he had really found one he shrank from going into the unknown darkness. If only there were another chap to talk to, to feel near! His teeth chattered with the cold, for he was soaking wet. But once more he remembered the Cub Law and did not give in.

“My light won’t last long if I keep it on,” he said. Flashing it round to see his way, he noticed a small lantern hanging on the wall with a box of matches in a little niche. With a sigh of relief he took it down and lighted it. The candle light cast weird, flickering shadows on the wall as Danny hurried on. Every now and then he lifted the lantern high, looking about him. He must have gone nearly a quarter of a mile when, some five feet above his head, a faint streak of pale light shone through a small, round hole in the wall.

“Daylight!” whispered Danny. “I wonder where that hole goes to.” Then he suddenly remembered his adventure of 1 A.M. on Sunday morning. “Why, that must be the drain-pipe telephone!” he said. “This is where the man was who listened at the other end of the pipe while the one in the ditch talked in a funny language!”