There was not much to see.  The great pool was very full ­a great, V-shaped sheet of water, or elongated triangle, whose shortest side was formed by the massive stone dam built across the narrow valley, standing some forty feet high from its base, to keep back the waters, and being naturally, when full, forty feet deep at its lower end.

Mr Willows and two men were at one end of the wall when Manners and the boys climbed on to it that afternoon, to stand in the middle looking up the valley over the long sheet of water to where it dwindled from some fifty yards wide to less than as many feet.

One of the upper sluices was opened, and though the great mill-wheel in its shed far below was going round at its most rapid rate, urged by the stream of water which passed along the chute, a good-sized fall was spurting out by the upper sluice.

These two exits were, however, not enough to keep the water down, so rapid was the flow from the hills to swell the stream, and the water in the great pool still rose.  Hence it was that the second sluice was to be opened, and in a few minutes a third rush added its roar to that of the other two.  Mr Willows stood watching for a few minutes, till he had satisfied himself by observing the painted marks upon a post that the water had ceased to rise, and then he walked away, leaving the others to chat with the men, who hung back for a few minutes after securing the sluice door, before going down to resume their regular work in the mill.

“Not much of a time for trout fishing, Mr Manners, sir,” said one of the men.

“No,” was the reply; “it is all over for the season for me.”

“Suppose so, sir.  Have you young gents been below there to have a look at the eel-box?”

“Eels?” said Manners.  “Ah, I like eels.”

“There’ll be plenty to-night, sir; they’ll be well on the move after sundown.  I shouldn’t be surprised if there was a good take.”

“We ought to be there to see,” said Will.  “The rains will have brought them down.  It’s rare fun catching the slippery beggars.  You’ll help, won’t you, Mr Manners?”

“Rather a slimy job,” was the reply; “but I’ll put on an old coat and pair of trousers, and come.  What time?”

“About eight o’clock.  That’ll do,” said Will.  “Then you can come in to supper afterwards with us.”

“Right!” was the reply; and that night, prompt to their time, Josh, who had called at the cottage on his way down, presented himself at the Mill House garden-gate with Manners, both properly equipped for their slippery task, and finding Will awaiting their arrival.

“Come on,” he cried; “I thought you didn’t mean to come.  I hate waiting in the dark.”

He led the way through the garden to the lower gate by the mill-yard, and then right along under the buildings to the huge shed built up over the wheel, which was turning rapidly to the hollow roar of the water descending the chute to pass into the many receptacles at the end of the great spokes, before falling with echoing splashes into the square, stone-built basin below.

It was close to the exit here that a portion of the great shed had been devoted to the purpose of an eel-trap, which was most effective in warm, rainy times when the flooded waters were full of washed-out worms such as the fat eels loved, but for which they often had to pay very dear, for it came to pass that they were often carried by the swift waters into the great stone chute.  Then, in all probability, their fate was sealed, for they would be borne along to the end, writhing and struggling in vain, only to be carried right over the turning wheel before falling into the great, square, stone opening below, where another rushing chute carried them onward into a stout, iron-barred cage whose bottom and sides were so closely set that only the very small could wriggle through.  The larger collected in a writhing cluster just where an iron, cage-like door could be opened, and a basket held to receive the spoil.

But this particular night, in spite of its promise, showed no performance.  The little party, lantern bearing, descended a flight of steps, hardly able to make each other hear, so great was the echoing splash going on around, and stopped at the bottom in a dank, dripping, stone chamber, close to the floor of the iron cage.

“How are you going to cook ’em, Mr Manners?” said Will, with his lips close to his companion’s ear.

“Some stewed, some spitchcocked, and the rest in a pie.”

“Then we’re not coming to dine,” cried Will, laughing, as he threw the light of the lantern upon the cage, where there was a wet gleam as something slowly glided round.

“Oh, what a shame!” cried Josh.  “Why, there’s only one!”

“Yes, only one,” said Will, “and it isn’t worth while to open this nasty, wet, slimy door for him.”

“Oh, but there’ll be some more,” cried Josh; “there’s plenty of time.  In about an hour there’ll be as many as we can carry.”

“But we are not going to wait in this dreary hole,” said Manners.  “I don’t enjoy eels when I’ve got a cold.”

“Oh, no,” cried Will; “we will go and have a bit of a walk, and come down again.”

They drew back from the eel-trap, Will leading the way, and made for a door in the huge shed, where the lantern was carefully extinguished and put on a ledge, before they stepped out into the dark night, the closing of the door behind them shutting in a good deal of the hollow roar, with its whispering echoes.  That which they listened to now was more splash, rush and hurry, as the wheel turned at greater than its usual speed, and the overladen dam relieved itself of its contents.

Still there was too much noise for easy converse, and they tramped on, Will with the intention of climbing to one of the narrow paths that led in the direction of the upper stream.

They were just on a level with the top of the stone dam, when Will stopped short.  The spot he had chosen for his halt was dark as pitch, for a clump of bushes overhung the way.

“What’s the matter?” said Josh, who came next.

“Be quiet,” replied Will.

“Anything wrong?” asked the artist, for they blocked his way.

“N-no,” replied Will, dubiously; “only thought I heard something.”

“Thought you heard something!” said Manners.  “There’s not much think about it.  My ears seem stuffed so full of sounds that I can hardly hear myself speak.  The rushing water and its echoes from up above seem to fill the air.  What did you think you heard?”

“That’s what I don’t know,” said Will, thoughtfully, with his lips close to the speaker’s ear; “and I can’t hear it at all now.  It was a dull, thumping sort of noise.”

“Echo,” said Josh.  “The wheel’s going so much faster round than usual.”

“N-n-no,” said Will; “it wasn’t like that.  I wish I could hear it again.”

“What for?” said Josh.  “What was the matter?  Here, I say, which way shall we go?  I know:  let’s go and see if any of the old owls are out beating the ivy for birds.”

“There,” cried Will, “that’s it!  You can hear it now!  Listen!”

All stood perfectly still for a few moments.

“Water, water everywhere, and far too much to drink,” said Manners, spoiling a quotation.  “I can’t hear anything else.”

“Oh, Mr Manners!  Why, there it is, quite plain.  You can hear it, can’t you, Josh?”

“Thumpety, thumpety, thump, thump, thump!” said Josh.  “Sounds like somebody beating a bit of carpet indoors.  Why, it’s only echoes.”

“Pooh!  What could make echoes like that?”

“The great axle of the wheel worked a little loose in its bearings through the weight of the water.”

“Nonsense!  Can’t be that.”

“All right!  What is it, then?”

“Don’t know, don’t care.  It’s a nocturnal noise, isn’t it, Mr Manners?”

“Well, it’s a noise,” said the artist, “as if someone was hammering with a wooden mallet.  I heard it quite plainly just now, and it seemed to come from below there, out of the darkness down at the bottom of the dam.”

“Oh, no,” cried Josh, “it was from right up yonder, ever so high.”

“No, no,” said Will; “it seemed to me to come from just opposite where we are standing now.”

“Echo,” said the artist, laconically.

“Yes,” said Will; “carried here and there by the wind.”

“Well,” said the artist, “the water makes roaring noise enough, without our listening for echoes.  Let’s go a bit higher where we can see the sky.  It’s horribly dark down here, but the stars are very bright if we get out of the shadows.  What’s the matter?” he said sharply, for Will caught his arm.

“There it is again,” cried the boy.  “Somebody must be hammering and thumping.  What can it be?”

“It’s what I said,” said Josh; “the bearings of the big wheel are a bit loose.  Who could be hammering and thumping in the darkness?  Wouldn’t he have a light?”

“I don’t know,” said Will; “but if something’s got loose, it ought to be seen to.”

“But you couldn’t do anything in the dark,” said Josh.  “My word, what a game it would be if the old wheel broke away!  What would happen then?”

“Once started, I should say it would go spinning down the valley for miles,” said Manners, laughingly.  “Just like a Brobdingnagian boy’s hoop gone mad.”

“Ah, I should like to see that by daylight,” cried Josh.

“I shouldn’t,” said Will, bitterly.  “It wouldn’t be much fun.  There! now, can you hear it?  That thumping?”

“Yes, I heard it then,” said Manners, “and I don’t think that there’s any doubt of its being the echo of something giving a thump as the wheel turns.  Is it worth while to go and tell old Jack-of-all-trades Drinkwater to come and see if anything’s wrong?”

“No,” said Josh.  “I don’t believe he’d come.”

“Perhaps it’s nothing to mind,” said Will, thoughtfully; “only, working machinery is such a ticklish thing.  There, I can’t hear it now.”

They stood listening for quite ten minutes, but the unusual sound was not renewed.

“Perhaps it’s somebody in the mill,” said Will.  “Let’s go down and look.”

“All right; anything to fill up time,” said Manners, “before we get my eels.  There’s no occasion to go up here.”

They descended cautiously through the darkness to the mill-yard, following Will, who made straight for the door leading into the machine-room, the fastening yielding to his hand, for few precautions were used in the shape of bar or bolt in that quiet, retired place; and, as the door swung back, the three stood gazing into the darkness before them, listening and feeling.  The whole building seemed to thrill with the vibration caused by the turning wheel, the weight of the water making the entire building quiver as if it were alive.

“Rather weird,” said Manners.  “I never was here before at such a time.  Does the place always throb in this way?”

“When the wheel is going fast,” replied Will, “it gently shakes the biggest beams.”

“Sounds as if it might shake the place down in time.”

“Oh, no,” said Will; “it’s too solid for that.”

“Well,” said Josh, “there’s nobody doing anything here.  If there was, there’d be a light.  It was only echoes.  Come along.”

“But if it was echoes,” said Will, “why did they leave off?”

“Not so much water coming down perhaps,” suggested Manners.  “There, isn’t it nearly time to go and see if there are any more eels?”

“Hardly,” replied Will, “but some might have come down.  It’s just as it happens.”

“Oh, yes,” said Josh.  “Sometimes there won’t be one in a whole night, and another time there’ll be pounds and pounds in half an hour.  It all depends upon whether they are on the move.”

They made for the lower door again at the bottom of the cage shed, and entered the hollow, dismal place.  Will felt for the lantern after closing the door, struck a match, and, to the artist’s satisfaction, the rays fell upon several slimy, gleaming objects beyond the bars; and after a good deal of splashing, writhing, and twining themselves in knots, the prisoners were secured in a dripping basket that had been held beneath the opening formed by drawing back the little grating.

“Capital!” cried Manners, eagerly.  “Why, there must be half a dozen pounds.”

“Nearer a dozen,” said Will.  “Look out, Josh!  Hit that chap over the head, or he’ll be out.”

Josh struck at the basket-lid, but a big, serpent-like creature had half forced its way through, to be down on the wet stone floor the next moment, making at once for the water a couple of yards away.

“Stop him, Mr Manners!  It’s the biggest one.  I can’t leave the basket.”

“And I can’t leave the light,” said Josh; but, as they spoke, the artist was in full pursuit, seeing as he did that a delicious morsel was going to save itself from being turned into human food.

There was a quick trampling faintly heard on the wet stone floor, followed by a rush, a glide, a heavy bump, and a roar of smothered laughter.

“Yes, it’s all very fine, young fellows,” growled the artist, as he gathered himself up; “a nasty, slimy beast!  I tried to stop him with my foot, and it was like the first step made in a skate.  Has it gone?”

“Gone?  Yes,” cried Josh.  “Never mind; there are plenty left.  They’re awful things to hold.  He would have got away all the same.”

“Not if I’d had a good grip,” said Manners.

“I don’t know,” said Will.  “He might have got a good grip of you.  Those big ones can bite like fun.  Are you very wet?”

“Bah!  Abominable mess.  This floor’s covered with slime.”

“Shall we stop any longer?”

“No,” said the artist; “I’ve had enough for once.  Let’s get out in the open air again, and try and find out what made your noise.”

In a few minutes they were back on the top of the great stone wall that held the waters back, listening in the darkness amidst the rush and roar of sluices and chute, supplemented by the distant thunder of the heavy falls high up the stream, for the peculiar thumping whose repetitions had caught Will’s ears.

But they listened in vain, and continued their way to Drinkwater’s cottage, where the basket with its living freight was placed, spite of the artist’s protests, in his landlady’s hands.

“Well, I suppose I must keep them,” said Manners, “and I will, for this is about the finish up of our games, lads, for this year.”

He spoke unconsciously.  It was; for as soon as the trio had passed from the dam on their way to the first zig-zag, from out of the darkness at one end of the dam the strange, weird noise began again.  It was as if heavy blows were being given upon some great iron tool.  Now and then they would cease, but only to go on again for quite two hours, till all at once a fresh sound arose ­a peculiar, whispering gurgle, which gradually gathered force, to go on increasing through the night; but not another blow was heard to fall.