"Till Monday then!" said Garth as Lawless stepped into the launch.  
"To-day week it is, sir!" returned the captain as Carstairs cast him the painter.
 
"You might fire the gun to let us know you're back," cried the baronet.
 
"Right-o!"
 
Lawless turned to bend over the engine. Then he looked round quickly and grinned.
 
"Good luck!" he cried, "and good hunting!" and waved a friendly hand. With that he pushed over the lever and with a mighty flurry of propeller and vast bustle among the sea-birds on the foreshore, the Naomi's launch throbbed her way out into the bay towards where, spanning as it seemed the harbour's narrowest part, a creamy band of white spume marked the surf-line. Silently we watched the pretty craft, her paint and brass-work flashing in the morning sun, gliding through the green water. Then Lawless raised an arm in a parting greeting, and the white launch melted into the spume and spray of the open sea.
 
We stood on a long sloping beach of gleaming white sand shut in on all sides save the sea by lofty grey rocks. Their jagged points out-topped the bright-green fronds of the waving palm-trees which grew almost down to the water's edge. Their column-like appearance, coupled with the singular silence of the island, gave me a sort of solemn feeling, like being in a cathedral.
 
Some three hundred yards from where the foam-crested rollers beat their thunderous measure on the beach, the ground rose abruptly. The sand ended and became emerged in a tangle of coarse grass. Alternating with a wild and luxuriant undergrowth of a great variety of tree ferns and other plants, it formed a kind of tasselling to a great curtain of greenery which rose, as it seemed, sheer from the sea.
 
The verdure was so dense that it completely hid the bases of the pointed cliffs which, clustered together like a bundle of faggots, formed the high central part of the island. From some hidden source a clear cold stream of water came plunging down from the cliff, rushing and gurgling until it lost itself in the sea.
 
It was the first time I had ever set foot on an uninhabited shore. It was a curious sensation. The sea-birds wheeled aloft with their harsh melancholy cries; among the trees above the beach there was sometimes the flash of a brilliantly-plumaged bird and here and there some animal rustled in the undergrowth. But otherwise a deep silence brooded over the island. There was an atmosphere of expectancy about the place which rather intrigued me.
 
I lost no time in setting about choosing a site for our camp. The appearance of the foreshore, exposed to the full force of the wind in unfavourable weather, did not impress me favourably, nor, owing to the danger from lightning in the thunderstorms that spring up so suddenly in these climes, did the obvious solution of erecting our huts under the shelter of the trees higher up on the shore commend itself. Moreover, I knew very little about conditions on Cock Island and, were there any wild animals about, it would be as well, I reflected, to pitch our camp in some spot not easily accessible to attack.
 
After exploring round a bit I came, behind a mantle of hanging creeper, upon the mouth of a cave. Set in the lofty grey rocks dominating the beach, it was well clear of high-tide level and clean and dry into the bargain. The roof sloped somewhat, but there was ample clearance for Garth's six feet when he stood erect and the cave ran back for some twenty feet into the rock.
 
So we plumped for the cave. Having stripped to vest and trousers, Garth and I started carrying up our stores from where the launch of the Naomi had deposited them on the beach. While we stacked the various boxes neatly at the back of the cave, Carstairs was busy fitting up what he called his "field-kitchen." Higher up the rocks, in a little cavity well-sheltered from the wind, he installed his Primus stove, cook-pots and other impedimenta.
 
It was with the utmost reluctance that I spared the time for this tiring but necessary fatigue. I was on fire to be off into the interior of the island and locate the grave. Garth, too, was as keen as mustard, and fairly jumped at my proposal that, as soon as the stores were stowed away, we should set forth on a voyage of discovery.
 
It was a long job; for the cases were heavy and the going was bad, but when I stood on the beach below and, with the roar of the ocean in my ears, looked up at our temporary home, I felt rather pleased. Absolutely no trace of our presence was discernible. Though I was aware that perhaps not one vessel in two years called at the island, I have always had a very healthy respect for the long arm of coincidence. I did not wish my investigations at Cock Island to become the mark of prying eyes.
 
It was past three o'clock and the sun very warm when Garth and I set out. We took with us a flask of cold tea apiece, some biscuits and some dates and a shot-gun each. With a wave of the hand to Carstairs, our guns slung across our backs, we plunged into the tangle of steep woods growing down to the shore.
 
The climate of the island seemed to be temperate enough. The air was a little steamy but mild and at first there was a pleasant breeze off the sea to cool us. To be equipped for the rocky nature of the island both of us had brought stout hob-nailed boots, and we praised our circumspection when we realised that only by boulder-climbing should we gain access to the higher parts of the island.
 
The climbing was arduous (for neither of us was in form) but not too difficult. I kept a sharp look-out for any traces of former visitors. Once I found some sheep droppings and again a large bleached bone which looked as if it might have come from a sheep. But of man there was no trace.
 
The scrub soon gave way to forest and for a good half hour we toiled up the jungle-clad slopes. Great trees formed an almost impenetrable roof over our heads through which the sunshine fell but sparsely. We went forward in a dim and mysterious twilight with no sounds in our ears other than the swift rushing of the stream which gave us our direction, our laboured breathing and the rattle of our nailed boots on the boulders. It was an eerie place which somehow filled me with misgivings.
 
Suddenly Garth, who was leading, gave a shout. He stood on the flat top of a rock, a dozen feet above my head, and pointed excitedly in front of him. I scrambled to his side.
 
We were looking down into a deep circular depression shaped like a basin. It reminded me of a quarry, but I imagine it was in reality the crater of some small extinct volcano. What had brought the shout to Garth's lips was the sight of a ruined hut which thrust its broken roof from out of a tangle of gigantic ferns.
 
So breathless were we with our climb that we were past speech. In silence we slithered and scrambled down into the hollow, the long tendrils of the plants twisting themselves round our legs and the thorns catching in our coats.
 
It was a rude timber shack with a door and a window, the interior choked roof-high with growing ferns. The timber flooring had rotted away and through the mouldering planks the jungle had thrust its shoots profusely as though to claim its own. But in one corner, where a roughly-carpentered bedstead of timber stood, some attempt had apparently been made to thin out the ferns for a space. On the bed there lay a rotting blanket; on the floor close by some empty canned beef tins red with rust. The blanket practically fell to pieces at the touch. It was not marked and, though we groped pretty thoroughly among the ferns, that was all we found in the hut.
 
"There's nothing here," I said at last. "Let's have a look round outside. I am wondering...."
 
The words died away on my lips. I had reached the hut door, my face turned towards the farther edge of the crater, the opposite side from that by which we had descended. A hundred and fifty yards from where I stood a large timber cross was planted in the ground. Between it and the hut lay a great isolated boulder which had probably concealed the cross from our view when we had climbed down into the hollow.
 
For a moment I could hardly speak. I have seen the proud loneliness of Cecil Rhodes' resting-place in the Matoppos; I have stood (like everybody else) in the amber light that bathes Napoleon's tomb "on the banks of the Seine among this French people I have loved so well." But I have never seen a sight more impressive than that solitary grave on that desert island set down beneath the little round canopy of blue sky which seemed to be borne by the lofty frowning cliffs towering all around. Beneath that plain wooden cross, I told myself, in a silence unbroken by Man, lies the Unknown. It was a mighty impressive thought.
 
A rudimentary path, still to be discerned through the all-pervading undergrowth, led, round the boulder of which I have spoken, to the cross. The grave lay out in the open in a little patch which had been cleared of ferns. As we came up to it I noted, with an odd little trick of the memory, that the grey and weather-beaten surface of the cross was highly polished, even as the beach-comber had described, by the action of the sand grains blown by the wind from the seashore.
 
Fashioned out of two baulks of timber wired together and solidly implanted in the ground, the cross stood at the head of a long hillock of earth. On the grave lay, face upwards, a small round mirror and, a little beyond it, an empty bottle, uncorked, which had fallen on its side.
 
"You see," I remarked to Garth, "it's just as Adams said!"
 
I stooped to pick up the mirror. Then to my surprise I saw that it was wired to a timber cross-piece which ran out from the cross as a support. It was a little glass set in a metal frame.
 
"It looks like a shaving-glass!" said Garth.
 
I did not undeceive him. I am not a secretive person by nature but by training. The very character of Intelligence work—the careful sifting of every apparently insignificant scrap of evidence, the lengthy process of surmise and deduction—tends to make one discreet, even when dealing with one's familiars, until a plain statement of fact can be drawn up. So I did not tell my host that, the moment I saw that the glass was attached to the cross, my brain leaped at the first clear clue to the Unknown's baffling cipher.
 
For the sight of the mirror, loosely wired so that it faced the foot of the grave, immediately brought into my mind the first line of that bewildering doggerel:
 
"Flimmer', flimmer' viel."
 
The reference to flashing surely indicated that the mirror was to be used as a heliograph. The next line—that about "the garrison of Kiel"—still utterly floored me; but, I reflected, since we had a heliograph, the fol............