“Now a little more to the left, I think,” said Holmes cheerfully.

Surely we were by-passing the Old Light and walking into the same quicksand that I had seen earlier? Yet it was still firm going and gradually I could just make out the ghostly contours of the Old Light with its heavy wooden supports and the round body of its barrack-room. Yet if that was so, then the beam which should have been directed out to the Boston Deeps was shining a little more in the direction of King’s Lynn. It was a discrepancy that might not be noticed at a distance where the beam was more widely reflected but was just enough to lead us a hundred yards out of our way across the mudflats. Was this not the sort of trick which a century earlier the wreckers had employed to decoy a ship on to the rocks and loot it?

Presently we found our way to the black-painted iron ladder and climbed it, the first ripples of the ebb swishing about our feet. Holmes lit the oil-lamp in the barrack-room. There was no policeman on guard on the sands below for the tide would soon have covered them. We should be undisturbed for several hours until the tide had turned and the Freiston relief arrived.

Holmes drew his silver flask from his pocket and the comforting spirituous aroma of whisky came to me as I sat down on one of the two black horsehair chairs. Reason returned where panic had prevailed.

“Roland Chastelnau was not the victim!” I exclaimed, “He was his brother’s murderer!”

Holmes said nothing. He was climbing the wooden ladder now into the lantern-room above us. There was a pause and then I heard his voice.

“It is as I supposed, though it was not obvious by daylight. The black metal shutters on the windows have been adjusted. The direction of the beam has been deliberately altered, not by much but enough to prove fatal. Any man trying to navigate the route back from the scene of the brothers’ struggle to the Old Light by using this beam would have walked into the river estuary with a floor tide running. Not the quicksands, Watson, but the river with its tidal undertow and currents.”

Then I saw the whole mystery clearly. Roland Chastelnau had decoyed his brother to the mudflats by a warning gunshot. There was a struggle, in which Roland had either died or escaped only to drown later on. The evidence of that was conclusive since this afternoon. But to make assurance doubly sure, before he went down to the beach leaving Abraham alone in the Old Light, Roland had moved the black iron shutters of the lantern in their grooves so that it shone several degrees or more in error.

No one who merely wound the mechanism, at the lower level, needed to climb to the top of the dome to check the iron shutters. The altered direction of the beam would not have been visible at all in daylight. To the Boston Deeps at night, it would be the usual distant glimmer. But whatever the outcome of the struggle on the beach, Roland intended that Abraham Chastelnau should never get back to the Old Light alive. The death which Holmes and I had avoided in the estuary at flood tide would have overtaken Abraham if all else failed.

Roland Chastelnau, had he escaped whatever death overtook him, need only have returned to the Old Light and slid the thin iron plates of the shutters to their original position. Roland cannot have expected that Mr Gilmore and his sexton should have seen the fight-or horseplay-on the sands but even that evidence was conclusive of very little. From the facts available, Abraham Chastelnau’s death would surely have been recorded as a tragedy of tide and darkness and of his own unaccountable miscalculation.

6

With that we have the whole story,“ I said, almost an hour later. By now the tide was rushing and swirling below us among the wooden legs of the barrack-room. Holmes looked at me thoughtfully.

“You are to be congratulated, Watson. It is your case and you have marshalled the facts in such a way that I am quite sure Inspector Wainwright and our friend Lestrade will be among the first to congratulate you upon your conclusions.”

There was something in his tone that I did not quite like, hinting a little too much at irony. Just then, however, I cared less about congratulations than the opportunity to sleep. There seemed to be no food in the barrack-room, other than cocoa made with hot water. However, I have long thought that a man can do without food for quite a while provided he has sufficient sleep-and he may do without sleep for a time so long as he is adequately fed. That being so, I made myself as comfortable as possible on the barrack-room bunk, which curved slightly to follow the wall of the lighthouse.

I was aware that Holmes was still moving about restlessly and I believe, before I fell into a deep sleep, that I was sufficiently conscious to know that he had made his way up the internal ladder to the lantern-room. I did not hear what he was doing, indeed he could have dismantled the entire lighthouse dome without disturbing me. When I woke again, it was after midnight and there was no further sound of water on the sand below us. By his own standards, Holmes had shown extreme patience in allowing me to sleep for what must have been an hour or two.

“Watson!” I think it was the sound of the bunk creaking which provoked this summons, “I should be obliged if you would come and give your opinion in a small matter.”

I sat up and looked for the shoes I had taken off. In a minute or two I climbed the ladder and was staring in some dismay at the dismemberment of the lantern-room clock-case. The mechanism was still functioning, so far as I could see, but Holmes had extracted several pieces of the wooden framework which were now lying on the log-book table.

It was plain that, as so often, he had not been to bed. His face was pale as parchment but his eyes in their dark sockets were all the brighter for that.

“Tell me, Watson, if you were possessed of some small treasure in such a place as this, where would you choose to hide it?”

“I suppose that would depend from whom I wanted to hide it.”

“From all the world-but most of all from your friends.”

“Holmes, is this some matter to do with the clockwork mechanism?”

“No. Why should it be?”

“Very well. I should not leave it in the drawers or cupboards. There are not many of them and it would quite soon be found. Perhaps I would hide it somewhere in the mechanism of the lantern but that mechanism must be in motion twenty-four hours every day and seven days every week throughout the year. Moreover, according to Wainwright, the lantern and the reflectors are usually cleaned every few days or so, even the panes of the glass dome are polished.”

“So far you have only explained where you would not hide it.”

“I should prefer a place where the mechanism which is never halted might conceal it. Since you have pillaged so much of the clock case, I suppose that is where I should choose.”

“Well done, Watson! We shall make a criminal investigator of you yet.”

I looked at the pieces of wood, the clutter of screws and little bolts, anonymous items of brass and iron on the table. Though the machinery which regulated the reflectors was working constantly, there were convenient spaces within the wooden case, as there are in any long case clock.

Holmes watched my eyes and read my thoughts.

“Put your hand up into the clock-hood, behind the dials and just below the drum that winds the clock-weight. You shall see what you shall see.”

I felt-and found a narrow wooden ledge that ran round four sides of the interior of the case.

“There is a ledge an inch or so wide but there is nothing on it.”

“What purpose does it serve?”

“There is nothing resting upon it. It helps to brace the structure, that is all.”

“Not of great interest?”

“I would hardly think so.”