Solar Pons stood up and went over to the fireplace; he kicked the fallen embers into life and Miss Grimstone hurried to put on some fresh wood to feed the little blaze.
"It soon became evident that the appearance of the phantom and its lightning disappearances could be explained by only one set of circumstances. My travels round the marsh made it self-evident that such appearances and disappearances would have to be extremely carefully engineered or the masquerader would rapidly end a victim himself.
"It merely meant that the apparition — created by a luminous chemical solution — was painted on one side of the hooded cloak only. The person wearing it would then merely have to turn his back on his victim to become invisible. Jessel put me on to it when he said the apparition disappeared as though someone had pulled down a blind. My deductions were proved right this evening in all respects when, as I suspected, I saw that the facial image strongly resembled Silas Grimstone himself."
"You cannot mean it!"
"I was never more serious, my dear fellow," said Solar Pons with a grim smile. "Our walk this morning and the conclusions I drew from the evidence presented to me, made it equally obvious that D'Eath Farm was the only conveniently situated building that would suit. Knight here could not only escape into the marsh but easily reach the main road. When I saw the padlocked door of the abandoned farm building and smelt the distinctive odor of phosphorus, my conclusions were hardened."
"What about your third point, Pons?" I asked.
"That was the most important of all. The entire deception was designed as an accusation; to appeal to old Silas Grim-stone's guilty conscience. He had to be convinced that he — and he alone — had seen a ghost. Unfortunately for our friend here, others became aware of the deception. Among them, Dr. Strangeways and the late Tobias Jessel."
Knight was already on his feet.
"I was not responsible for Jessel's death, Mr. Pons! I swear I only intended to frighten Grimstone into a confession."
"I am well aware of that," said my friend gently. "Jesse! undoubtedly fell into the water in a drunken stupor."
"What about the cuts on his hands, Pons?' I asked.
Pons shook his head.
"The wounds were made by the jagged edges of the broken ice."
Solar Pons turned away from Miss Grimstone and Knight, who slowly resumed his seat.
"To get back to my point, Parker. I strongly suspected that the so-called phantom had carefully prepared his scheme and that he wished only Grimstone to see the figure he had created. You may remember I was particularly careful to ask Grimstone about the circumstances when both he and his niece saw the apparition."
"I remember, Pons."
"You will recall that Miss Grimstone suddenly appeared from behind a fringe of bushes, and I commended that fact to you. Knight did not even know she was there. In fact he was himself frightened by her sudden shriek and immediately ran off. Is that not so?"
"Indeed, Mr. Pons."
Knight lowered his head and looked the very figure of contrition. I shot a puzzled glance at Pons and then at Miss Grimstone, who sat behind the coffee pot with tightly compressed lips. The.clock ticked sonorously in the corner and it seemed impossible that the incredible drama of an hour ago had taken old Silas Grimstone so dramatically from us.
"You may remember also, Parker, that I was particularly intent on discovering the circumstances of the phantom's appearances to the old man. No true apparition, if such a thing existed, would make a noise when it appeared or disappeared; therefore, it was manufactured. We have already dealt with the matter of any traces it made being swallowed up by the mud and water, though there was enough evidence from the reeds and broken grasses to establish the passage of some heavy body. The zigzagging motion the thing made was because Knight had to keep to the firm paths to avoid being sucked under.
"You may also recall, Parker, I took some trouble when we were out on the marsh, in examining the dyke near Grimstone Manor, the spot where both old Grimstone and Tobias Jessel had their frightening experiences with the fiery blue figure. Jessel was not meant to see the phantom. Knight was hanging about in his guise, down below the dyke, waiting to see if old Grimstone was corning out. He did not hear Jessel walking along the road above and thus blundered on him accidentally. I submit that this reading is correct as I could not hear your footsteps, Parker, when I was at the foot of the bank, a long way below the level of the road."
"You are perfectly correct," said Knight with a groan. "It happened exactly as you said. And I can swear that I was nowhere near old Jessel on the night of his death."
"I believe you," said Solar Pons slowly. "And can so testify to the police if necessary."
I looked at my companion in amazement.
"This case began with a client being terrified by a phantom, and now it appears to be ending with the client as the villain and the attempted murderer as an innocent man!"
"Does it not, Parker," remarked Solar Pons with a dry chuckle.
There was silence for a brief moment. It was broken by Knight who seemed to be recovering his spirits as Pons proceeded.
"How did you come to suspect me?"
"I had a good many people who might have superficially fitted the bill," said Solar Pons. "They included Dr. Strangeways and a farmer on the marsh; our man might even have been concealed in a party of walkers who descended on the village. But I was looking for a young and active man; one who had a strong motive for treating old Grimstone so; one who had mastered all the paths and tracks of the marsh."
I looked at Pons in rising irritation.
"But how on earth could you have reasoned all this? We hardly knew Mr. Knight."
Solar Pons smiled, sending out a stream of aromatic blue smoke toward the ceiling.
"All this came to me very slowly old friend. And there was not a great deal of data to go on. But when I inspected the hotel register and found that Mr. Knight had come to The Harrow in September, only a few weeks before the ghostly manifestations began, my suspicions began to crystallize. Then, when Mr. Knight boldly introduced himself and I was able to study him close at hand, I immediately saw light. It was a master stroke, Mr. Knight, to make such a dramatic entrance, though there was some risk that Dr. Strangeways might have examined your supposedly injured ankle."
To my astonishment Knight gave a low chuckle.
"There is no getting around you, Mr. Pons. I reasoned, quite correctly, as it turned out, that Strangeways would not want to be bothered with anything so trivial, especially as he was enjoying a social evening at the hotel. Where did I go wrong?"
Solar Pons smiled thinly.
"When you came into the saloon you were limping with the right leg. The following morning, when we saw you just after breakfast, you limped on the left."
I looked thunderstruck at Pons. Even Miss Grimstone had to smile.
"But why all this masquerade and why the limp?"
"To provide an alibi, Parker," said my companion patiently. "An injured man could not leap agilely about the marsh in that fashion. The solution came to me rather late. It was the facial resemblance, you see."
"Facial resemblance, Pons?"
Solar Pons nodded dreamily, his eyes half-closed.
"Unless I miss my guess, Mr. Knight is a close relative of Silas Grimstone. I would hazard his nephew."
Miss Grimstone closed her eyes and appeared much moved by the disclosure. She breathed heavily.
"You are perfectly right, Mr. Pons."
"But why would Grimstone's nephew want to drive him out of his wits?" I cried somewhat wildly.
"One of the oldest motives known to mankind, Parker.-Revenge. Miss Grimstone herself supplied the missing fragments of my pattern on the marsh this morning. She said that Jethro Grimstone, the partner in the firm, went to Australia many years ago. It can never be proved now but I submit that his body is lying out there in the depths of the marsh somewhere. Mr. Knight — or rather Mr. Grimstone here — had come back from Australia and decided to take the law into his own hands to obtain a confession from his uncle. He would need an accomplice for that, Miss Grimstone, would he not?"