She made no reply but stared at him, as if one or the other of them had gone mad. Holmes continued.
“We are asked to believe that your brother Abraham, at the allotted time of no later than 7.45 on Sunday evening, cranked up the chain of the lantern mechanism in the Old Light at Sutton Cross. At the same time, he must have wound up the clock and the governor which controls the mechanism in order that it should continue to run correctly. Somewhen soon after that, he was summoned by a gunshot from the darkened beach. We do not know precisely what happened there between your brothers but soon afterwards Roland Chastelnau died. We presume that he drowned, from whatever cause.”
“I know that, Mr Holmes,” she said with quiet reproach.
“Abraham, it appears, attempted to return to the lighthouse. That should have been straightforward enough. However, it is alleged that Roland meant to ensure, whatever happened on the beach, that his elder brother should never reach the Old Light alive. Earlier that day, he had therefore adjusted the position of the iron shutters across the glass panes of the lantern dome. No one would have gone up there to check them, for the glass was cleaned that morning. No one would have seen the direction of the beam by daylight.”
She was holding a pocket handkerchief to her mouth and her head was bowed.
“The truth, Miss Chastelnau, is best. The altered direction of the beam, shining through the darkness a little closer to King’s Lynn and further from the Boston Deeps, was surely intended to lure its victim into the estuary and the quicksands. That would explain why his body was never found. If Roland had succeeded in such a plot, he had only to return to the Old Light as the tide ebbed and adjust the shutters to their original position. Unfortunately, he himself was drowned before the ebb. The misalignment of the shutters was therefore discovered by Dr Watson and myself. That was intended to be conclusive evidence of Roland’s guilt.”
“Intended?” she cried, looking up suddenly, “I do not understand. What Dr Watson has just told me is surely the truth.”
“And I have to tell you that it is quite impossible.”
“Why?”
“For two very simple reasons. Abraham could not have wound that clock at a quarter to eight, or at any time until after nine o’clock. Look at any simple grandfather clock, which the face of this one resembles. There are two keyholes which are covered when the hour hand is between the numerals for three and four-or eight and nine. The clock cannot be wound during those periods.”
“It may have been done earlier!”
“When the mechanism of the Old Light was inspected on the following morning, the timer had run down, as it would do after eight hours. The chain would be too heavy for the man who had to crank it up again if it ran longer. Indeed, the skipper of a collier in the Deeps noted in his log at quarter past five that morning that the signal of the Old Light was no longer being transmitted.”
“What has that to do with it?” she insisted.
“It has this to do with it, Miss Chastelnau. This indication of foul play was not that the beam of light failed after five o‘clock but that it had not stopped before. Had the mechanism been wound as early as eight o’clock the previous evening, the hour hand would then cover the keyhole until after nine. Next morning, the mechanism would have stopped and the Old Light would have failed an hour and a quarter earlier than it did. Someone had returned to the Old Light and wound the mechanism an hour or more after Abraham Chastelnau went down to the sands in response to his brother’s gunshot.”
She stared at him now with a look of dread which came from trying to guess how much more he knew.
“What happened on the beach,” he continued, “may be murder, accident, or misadventure. We can only be sure that Roland drowned, from whatever cause. Abraham lived and knew his brother was lost. He returned safely to the Old Light at about nine o’clock.”
“Why was he not trapped in the river by the altered beam of light?” I asked.
“Because it had not yet been altered. Whatever the cause or the outcome of the struggle on the sands, Abraham believed that he might face trial and execution for his brother’s death. He had not a single friendly witness to prove that he was guilty only of innocent self-defence, rather than premeditated murder. No one to prove that it was not he but Roland who fired the shot which signalled the beginning of the tragedy. Afterwards, he sat alone in the barrack-room, no doubt in distress and dread. He was alive and Roland was dead. He had very probably seen two figures on the church tower, witnesses of the struggle. The sound of the sexton’s rook rifle confirmed it.”
Neither of us spoke and Holmes continued.
“Who will believe him? He sees the stern-faced officers setting out from King’s Lynn.! He sees the dock at the assizes and the black cap put on by the judge who assures him that he will be hanged by the neck until he is quite dead. Worst of all, he sees the dreadful weeks in the condemned cell, hears the hangman’s knock and imagines the last walk across the prison yard to the tall shed with its thirteen steps leading up to the waiting noose.”
At last there was a sob from Miss Chastelnau. Holmes ignored her.
“The Old Light became a trap as the tide rose. He had only minutes to escape before the flood cut him off from the land. He went up to the lantern-room and wound the mechanism. It must run for as long as possible to conceal his absence. Then he altered the iron shutters to misdirect the beam of white light so that he might appear to have been its victim. Desperation sometimes breeds inspiration. You follow me? Those who inquired into the mystery would of course find the shutters altered. With luck, however, Roland would be found drowned. Abraham would have vanished. Where else was he but deep in the shivering sands, lured there by someone who had altered those shutters? What other man could have done that but his brother? Abraham would be searched for no longer. He did all this and then he made his escape across the fens or the beach, as the tide filled the sandbank under the Old Light. He knew that the longer he was missing, the more certain it would seem that he had been decoyed into the quicksands by the river’s edge and had died in their embrace.”
“Suppose Abraham set the trap of the shutters for Roland?” I asked.
“Then Abraham need not have fled. Accidental death by drowning would be the verdict. Abraham need only slide the shutters back to their usual angle and there would be no case against him. This is something more.”
“And what of the evil that he confessed to?” I asked, “What has he done?”
“I cannot tell you in his absence. I beg you, Miss Chastelnau, bring him in. I promise that I wish no ill to either of you and that I will help you if I can.”
This was extraordinary! Had Sherlock Holmes tracked down a murderer only to offer him help?
The poor woman at the centre of the drama stood up and went to the door. Almost at once she returned, followed by a tall loose-limbed man with a ruddy complexion. He did not look like a fellow of great intelligence as his eyes flicked at each of us in turn. Holmes stood up and held out his hand.
“Mr Abraham Chastelnau?”
Miss Chastelnau intervened, as if protecting a wild animal from those who hunted it.
“My brother watched you come into the hall and feared that you were police officers who had come for him.”
“No,” said Holmes calmly, “he need not fear that. Pray, Mr Chastelnau, stand over here in the bay of the window. Face the light. Watson too, if you please. Have no fear, Abraham, my friend is a doctor. Perhaps he is the doctor for whom you composed your letter, and then could not bring yourself to send it.”
I stared at Chastelnau’s face. It was strong-featured but round. The jaw-bone and, indeed, the neck had been disfigured by small and inflamed lumps or swellings, long healed over. I would have expected to find similar marks on his chest and shoulders, had I examined them. The infections had come, suppurated and healed over but they had never disappeared.