"Perhaps it can only be operated from below," Warrender suggested. "If this is an entrance to the cellar, it may be left open when any one comes this way."

"That's not likely. An entrance that can only be opened from one side isn't worth much. No, something sticks, and if that fellow went through a few minutes ago, it can't be for want of use. _Why_ does it stick, then?"

Armstrong pondered for a few moments, then said suddenly, "Possibly it's my pressure on the stone. Let's try."

He moved back, so that the weight of his body bore upon the rear instead of the fore end of the stone. Then, however, he found that he could not reach the hand-grip.

"Why not try the other side?" said Warrender. "There may be another grip there."

The other side of the staircase was open to the cellar, and Armstrong was able to thrust his arm into the aperture below the step without treading on the flagstone.

"Got it!" he said, a moment later. "There's a grip here. It moves in a quarter-circle. Something--a disk of stone, I fancy--is revolving."

He pressed on the flagstone; still there was no distinct movement downwards, though it seemed to have yielded a trifle.

"Clearly it won't shift until the other grip is turned," he said. "But how to get at that?"

After a little consideration he had another idea. Going a few steps up the staircase, he turned, and crawled down head first until he was able to get his hand under the edge of the stone.

"All right, old man," he said, cheerfully. "I've moved the grip now.

Keep clear of the other end of the stone."

Lying full stretch on the staircase, he pressed on the stone beneath him. It sank gently; the other end moved upwards, and in a few seconds the stone stood upright in the middle of a dark gap. Warrender bent down, holding the electric torch just above the opening.

"The bottom's only about five feet deep," he said. "It's the end of some sort of pa.s.sage. Come down, old man, and we'll explore it together."

[Ill.u.s.tration: "'THE BOTTOM'S ONLY ABOUT FIVE FEET DEEP.'"]

They dropped lightly into the cavity. By the light of the torch they saw that on each side a flat circular wheel of stone, lacking one quadrant, moved on an iron axle in such a way that a half-turn of the hand-grip removed the support of the flagstone and allowed the corner to drop down. The flagstone was nicely balanced on a revolving iron rod let into a socket at each end. This contrivance formed the entrance to a narrow tunnel about four feet wide, and something over five feet high in the centre. Neither of the boys could stand upright in it. The floor was of hard-beaten earth; the walls and the arched roof were of ancient brick, covered with an incrustation of slimy moss.

"An old smugglers' tunnel, I'll be bound," said Armstrong. "It will be very odd if we have struck a lair of modern smugglers. Just look at your compa.s.s and see what direction it takes."

The needle swung almost perpendicular to the course of the tunnel.

"Eastward," said Warrender. "That's strange. I thought it probably ran south, to somewhere near that place at the end of the island where we saw the marks of a boat the other day."

"It seems to shelve downward slightly. Looks as if it runs under the channel."

"Towards Pratt's uncle's grounds. Let's explore."

"Better switch off your light, then. We can find our way in the dark by touching the sides."

They went forward in single file, stepping gingerly, and bending their heads to avoid the roof. The air smelt musty and dank, and was unpleasant and oppressive. For a time the floor sloped gently downwards, but presently they were aware that it had taken an upward trend.

"We've crossed the channel," said Armstrong in a whisper that the vaulted walls made unnaturally loud.

A little later they noticed ahead of them a s.p.a.ce dimly illuminated.

Moving forward cautiously, they found themselves at the bottom of a circular shaft. Far above them they saw daylight in parallel streaks.

"A dry well," murmured Warrender, "roughly boarded over." Consulting his compa.s.s, he added, "Still eastwards. Rummy if the tunnel goes to the Red House."

Pursuing their way in utter darkness as before, the floor still rising very slightly, they became aware by and by that the tunnel had enlarged.

From the centre they could not touch the wall on either side, and the greater lightness of the air gave them a sense of s.p.a.ciousness.

Suddenly Armstrong, who was leading, stumbled over something on the floor and fell forward. His hands, instinctively thrust out, were arrested by a bundle encased in tarpaulin. He straightened himself. For a moment or two they waited, straining their ears. There was no sound.

"A light," murmured Armstrong.

The light revealed that they had arrived at a small chamber about twelve feet square and seven or eight feet high. The farther end was broken by the tunnel. In each side wall, a foot below the roof, were let a couple of iron rings, deeply rusted.

"For holding torches," said Armstrong.

The chamber was empty except for three bundles on the floor. It was over one of these that Armstrong had stumbled. Two of them were completely covered with tarpaulin, and roped; the third was partly open at the top.

"They're like the bundles I saw Rush and the other fellow carry up from the boat," said Armstrong.

"Queer smuggling," said Warrender, bending over the open bale. "It seems to hold nothing but paper."

He took up the topmost sheet. It was a thin, semi-transparent paper, and crackled to the touch.

"This isn't newspaper," he said.

"Cigarette paper, perhaps," said Armstrong. "But where's the 'baccy?"

"Can't smell any. I wonder how much farther the tunnel goes?"

Entering it at the extreme end of the chamber, Warrender came within a yard to a contrivance similar to that which gave access from the cellar.

"Here's the end," he said. "Look, the grips are turned. Shall we risk lifting the stone?"

"Dangerous," said Armstrong. "Goodness knows where we'd find ourselves."

Scarcely had he spoken when from above came the dull sound of footsteps.

Switching off the light, Warrender backed into the chamber and hastily crossed it with Armstrong, both moving on tiptoe. They re-entered the tunnel, crept along for a few yards, then halted, listening breathlessly. They heard the footsteps of one man in the chamber they had just left. The footsteps ceased, and were followed by a rustling.

It seemed clear that their presence was unsuspected, and they ventured to tiptoe back until, near the opening of the tunnel, they were able to peep into the chamber. By the dim light that came through the aperture left open by the revolved flagstone on the farther side, they saw a short, stout man drawing sheets of paper from the opened package. He counted them as he took them up, and presently turned, carried them through the opening, and let down the flagstone behind him. There was not light enough by which to identify him.

[Ill.u.s.tration: "THEY SAW A SHORT, STOUT MAN DRAWING SHEETS OF PAPER FROM THE OPENED PACKAGE."]

The boys re-entered the chamber, and listened until the sound of his retreating footsteps above had died away. Then Warrender switched on the light, took a sheet of paper from the top of the bale, folded it, and put it into his breast pocket.

"Now for home," he whispered. "We've something for Percy to start a new theory on."

CHAPTER XVI

WATERMARKS