When they reached Riversbrook they entered the carriage drive and traversed the plantation until they stood on the edge of the Italian garden facing the house. The gaunt, irregular mansion stood empty and deserted, for Miss Fewbanks had left the place after her father's funeral, with the determination not to return to it. The wind whistled drearily through the nooks and crannies of the unfinished brickwork of the upper story, and a faint evening mist rose from the soddened garden and floated in a thin cloud past the library window, as though the ghost of the dead judge were revisiting the house in search of his murderer. The garden had lost its summer beauty and was littered with dead leaves from the trees. The gathering greyness of an autumn twilight added to the dreariness of the scene.

"Kemp didn't say how far he stood from the house," said Crewe, "but we'll assume he stood at the edge of the plantation—about where we are standing now—to begin with. How far are we from that library window, Chippenfield?"

"About fifty yards, I should say," said the inspector, measuring it with his eye.

"I should say seventy," said Rolfe.

"And I say somewhere midway between the two," said Crewe, with a smile. "But we will soon see. Just hold down the end of this measuring tape, one of you." He produced a measuring tape as he spoke, and started to unwind it, walking rapidly towards the house as he did so. "Sixty-two yards!" he said, as he returned. He made a note of the distance in his pocket-book. "So much for that," he said, "but that's not enough. I want you to stand under the library window, Rolfe, by that chestnut-tree in front of it, and act as pivot for the measuring tape while I look at that window from various angles. My idea is to go in a semicircle right round the garden, starting at the garage by the edge of the wood, so as to see the library window and measure the distance at every possible point at which Kemp could have stood."

"You're going to a lot of trouble for nothing, if your object is to try and prove that he couldn't have seen into the window," grunted Inspector Chippenfield, in a mystified voice. "Why, I can see plainly into the window from here."

Crewe smiled, but did not reply. Followed by Rolfe, he went back to the tree by the library window, where he posted Rolfe with the end of the tape in his hand. Then he walked slowly back across the garden in the direction of the garage, keeping his eye on the library window on the first floor from which Kemp, according to his evidence, had seen Sir Horace leaning out after Holymead had left the house. He returned to the tree, noting the measurement in his book as he did so, and then repeated the process, walking backwards with his eye fixed on the window, but this time taking a line more to the left. Again and again he repeated the process, until finally he had walked backwards from the tree in narrow segments of a big semicircle, finishing up on the boundary of the Italian garden on the other side of the grounds, and almost directly opposite to the garage from which he had started.

"There's no use going further back than that," he said, turning to Inspector Chippenfield, who had followed him round, smoking one of Crewe's cigars, and very much mystified by the whole proceedings, though he would not have admitted it on any account. "At this point we practically lose sight of the window altogether, except for an oblique glimpse. Certainly Kemp would not come as far back as this—he would have no object in doing so."

"I quite agree with you," said Inspector Chippenfield. "He would stand more in the front of the house. The tree in front of the house doesn't obstruct the view of the window to any extent."

The tree to which Inspector Chippenfield referred was a solitary chestnut-tree, which grew close to the house a little distance from the main entrance, and reached to a height of about forty feet. Its branches were entirely bare of leaves, for the autumn frosts and winds had swept the foliage away.

Rolfe, who had been watching Crewe's manoeuvres curiously, walked up to them with the tape in his hand. He glanced at the library window on the first floor as he reached them.

"Kemp could have seen the library window if he had stood here," he said. "I should say that if the blind were up it would be possible to see right into the room."

"What do you say, Chippenfield?" asked Crewe, turning to that officer.

Inspector Chippenfield had taken his stand stolidly on the centre path of the Italian garden, directly in front of the window of the library.

"I say Kemp is a liar," he replied, knocking the ash off his cigar. "A d——d liar," he added emphatically. "I don't believe he was here at all that night."

"But if he was here, do you think he saw Sir Horace leaning out of the window?"

"I don't see what was to prevent him," was the reply. "But my point is that he was a liar and that he wasn't here at all."

"And you, Rolfe—do you think Kemp could have seen Sir Horace leaning out of the window if he had been here?"

"I should say so," remarked Rolfe, in a somewhat puzzled tone.

"I am sorry I cannot agree with either of you," said Crewe. "I think Kemp was here, but I am sure he couldn't have seen Sir Horace from the window. Kemp has been up here during the past few days in order to prepare his evidence, and he's been led astray by a very simple mistake. If a man were to lean outside the library window now there would not be much difficulty in identifying him, but when the murder took place it would have been impossible to see him from any part of the garden or grounds."

"Why?" demanded Inspector Chippenfield.

"Because it was the middle of summer when Sir Horace Fewbanks was murdered. At that time that chestnut-tree would be in full leaf, and the foliage would hide the window completely. Look at the number of branches the tree has! They stretch all over the window and even round the corners of that unfinished brickwork on the first floor by the side of the library window. A man could no more see through that tree in summer time than he could see through a stone wall."

"What did I tell you?" exclaimed Inspector Chippenfield in the voice of a man whose case had been fully proved. "Didn't I say Kemp was a liar? We'll call evidence in rebuttal to prove that he is a liar—that he couldn't have seen the window. And after Holymead is convicted I'll see if I cannot get a warrant out for Kemp for perjury."

"And yet Kemp did see Sir Horace that night," said Crewe quietly.

"How do you know? What makes you say that?" The inspector was unpleasantly startled by Crewe's contention.

"He was able to describe accurately how Sir Horace was dressed—for one thing," responded Crewe.

"He might have got that from Seldon's evidence," said Inspector Chippenfield thoughtfully. "He may have had some one in court to tell him what Seldon said."

"You do not think Lethbridge would be a party to such tactics?" said Crewe. "No, no. One could tell from the way he examined Seldon and Kemp on the point that it was in his brief."

"But the fact that Kemp knew how Sir Horace was dressed doesn't prove that he saw Sir Horace after Holymead left the house," said Rolfe. "Kemp may have seen Sir Horace before Holymead arrived."

"Quite true, Rolfe," said Crewe. "I haven't lost sight of that point. I think you will agree with me that there is a bit of a mystery here which wants clearing up."

They drove back to town, and, in accordance with the arrangement Crewe had made with Mr. Walters before leaving the court, they waited on that gentleman at his chambers in Lincoln's Inn. There Crewe told him of the result of their investigations at Riversbrook. Mr. Walters was professionally pleased at the prospect of destroying the evidence of Kemp. He was not a hard-hearted man, and personally he would have preferred to see Holymead acquitted, if that were possible, but as the prosecuting Counsel he felt a professional satisfaction in being placed in the position to expose perjured evidence.

"Excellent! excellent!" he exclaimed, rubbing his hands with gratification as he spoke. "Knowing what we know now, it will be a comparatively easy task to expose the witness Kemp under cross-examination, and show his evidence to be false." Mr. Walters looked as though he relished the prospect.

It was arranged that Inspector Chippenfield should be called to give evidence in rebuttal as to the impossibility of seeing the library window through the tree, and that an arboriculturist should also be called. Mr. Walters agreed to have the expert in attendance at the court in the morning.

But Crewe had something more on his mind, and he waited until Chippenfield and Rolfe had taken their departure in order to put his views before the prosecuting counsel. Then he pointed out to him that to prove that Kemp's evidence was false was merely to obtain a negative result. What he wanted was a positive result. In other words, he wanted Kemp's true story.

"You do not think, then, that Kemp is merely committing perjury in order to get Holymead off?" asked Walters meditatively. "You think he is hiding something?"

Crewe replied, with his faint, inscrutable smile, that he had no doubt whatever that such was the case. He thought Kemp's true story might be obtained if Walters directed his cross-examination to obtaining the truth instead of merely to exposing falsehood. It was evident to him that Kemp had come forward in order to save the prisoner. How far was he prepared to go in carrying out that object? When he was made to realise that his perjury, instead of helping Holymead, had helped to convince the jury of the prisoner's guilt, would he tell the true story of how much he knew?

"My own opinion is that he will," continued Crewe. "I studied his face very closely while he was in the box to-day, and I am convinced he would go far—even to telling the truth—in order to save the only man who was ever kind to him."

Walters was slow in coming round to Crewe's point of view. He had a high opinion of Crewe, for in his association with the case he had realised how skilfully Crewe had worked out the solution of the Riversbrook mystery. But he took the view that now the case was before the court it was entirely a matter for the legal profession to deal with. He pointed out to Crewe the professional view that his own duty did not extend beyond the exposure of Kemp's perjury. It was not his duty to give Kemp a second chance—an opportunity to qualify his evidence. He believed the defence had called Kemp in the belief that his evidence was true, but the defence must take the consequences if they built up their case on perjured evidence which they had not taken the trouble to sift.

Crewe entered into the professional view sympathetically, but he was not to be turned from his purpose. He felt that too much was at stake, and he lifted the discussion out of the atmosphere of professional procedure into that of their common manhood.

"Walters, I know you are not a vain man," he said, earnestly. "A personal triumph in this case means even less to you than it does to me. I have built up what I regard as an overwhelming case against Holymead. But it is based on circumstantial evidence, and I would willingly see the whole thing toppled over if by that means we could get the final truth. This man Kemp knows the truth, and you are in a position in which you can get the truth from him. It may be the last chance anyone will have of getting it. Apart from all questions of professional procedure, isn't there an obligation upon you to get at the truth?"

"If you put it that way, I believe there is," replied Walters slowly and meditatively. There was a pause, and then he spoke with a sudden impulse. "Yes, Crewe; you can depend on me. I'll do my best."