“And now, dear brother,” he remarked, gently closing the door, “we will resume our little discussion where we left off. I was, if you remember just about to ask you to sample the temperature of the furnace at 2,000° when the interruption occurred. Is it necessary that I should repeat that request, or was your experience at the lower temperature sufficient for you?”

Professor Goodman raised his haggard face and stared at his tormentor.

“What have you done to that poor young man, you devil?”

Mr. Robinson smiled and stroked his whiskers.

“Well, really,” he answered mildly, “I think the boot is on the other leg. The question is more what has he done to my unfortunate staff? Poor Mr. Freyder I feel almost certain must be in great pain with his face, judging by the noise he made, and two of my other servants have very nasty burns.”

“I know all that,” said the other. “But what has sent him insane?”

Mr. Robinson smiled even more gently.

“As a scientist, dear brother, you should know the tiny dividing line between sanity and madness. One little link wrong in that marvellous mechanism of the brain, and the greatest thinker becomes but a babbling fool. Not that his best friends could ever have called poor Drummond a great thinker, but”⁠—he paused to emphasise his words⁠—“but, dear brother, he serves as a very good example of what might happen to one who is a great thinker.”

Professor Goodman shivered; there had been no need to emphasise the meaning underlying the words.

“You see,” continued Mr. Robinson, “Drummond very foolishly and very unfortunately for himself has again crossed my path. This time, as a matter of fact, it was by pure accident. Had you not lunched with him on the day of your death and given him the notes of your process, you may take it from me that this little interlude would never have occurred. But you did⁠—and, well, you see what has happened to Drummond. The silly young fellow is quite mad.”

“You have done something to him to make him so,” said the other dully.

“Of course,” agreed Mr. Robinson. “Or to be strictly accurate, Freyder has.”

And suddenly Professor Goodman rose to his feet with a pitiful little cry.

“Oh! my God! I don’t understand. I think I’m going mad myself.”

For a moment or two Mr. Robinson looked at him narrowly. If such an appalling eventuality as that happened, the whole of his scheme would be frustrated. True, it was a common figure of speech, but Professor Goodman was a frail old man, accustomed to a sedentary life. And during the past two or three days his life had been far from sedentary. Supposing under the strain the old man’s reason did snap.⁠ ⁠… Mr. Robinson drew a deep breath: the mere thought of such a thing was too impossible to contemplate.

But it had to be contemplated, and it had to be taken into account in his immediate course of action. Whatever happened, Professor Goodman’s intellect must be preserved at all costs. Even a nervous breakdown would constitute a well-nigh insuperable obstacle to his plans. And in spite of the seriousness of the position, Mr. Robinson could hardly help smiling at the irony of the thing.

Here was he with the greatest prize of his career waiting to be picked up⁠—almost, but not quite, within his grasp. All the difficult practical details, all that part of his scheme concerned solely with organisation, had gone without a hitch. And now he was confronted by something far smaller in comparison, and yet almost as important as all the rest put together⁠—the state of the mind of an elderly scientist. It was a problem in psychology which in the whole of his career he had never had to face under exactly similar conditions.

There had been occasions when men’s reasons had snapped under the somewhat drastic treatment with which Mr. Robinson was wont to enforce his wishes. But on all those occasions a remarkable aptitude with the pen had enabled him to dispense with the formality of their signature. This time, however, his wonderful gifts as a forger were wasted. Knowledge of ancient cuneiform writing might have been of some use in enabling him to decipher the notes, he reflected grimly⁠—but as it was they were hopelessly and utterly unintelligible. Only Professor Goodman could do it, and that was the problem which had just come home to him more acutely than ever. What was the best line to adopt with the old man? How far would it be safe to go in a policy of threats and force? Or would apparent kindness do the trick better and quicker? Especially quicker⁠—that was the important thing. It was a ticklish point to decide; but it was essential that it should be decided, and at once.

He glanced at the haggard, staring eyes of the man confronting him; he noted the twitching hands, and he made up his mind. After all, it was easy to go from kindness to threats, whereas the converse was difficult. And though he had reluctantly to admit to himself that burning a man’s arm on red-hot metal can hardly be regarded as the act of a personal friend, there was no good worrying about it. It had been done, and could not be undone. All that he could do now was to try to efface the recollection of it as far as possible.

“Sit down, Professor,” he said gently. “I feel that I owe you some explanation.”

With a groan the other sank back into his chair.

“Will you have a cigar?” went on Mr. Robinson easily, holding out his case. “You don’t smoke? You should. Most soothing to the nerves. In the first place I must apologise for not having made things clearer to you before, but this slight contretemps with Drummond has kept me rather fully occupied. Now I want you to recall to your mind the interviews that you had with Sir Raymond Blantyre.”

“I recall them perfectly,” answered the Professor, and Mr. Robinson noted with quiet satisfaction that he seemed to be less agitated.

“He offered you, did he not? a large sum of money for the suppression of your secret, which you refused⁠—and very rightly refused. But, my dear Professor, do you really imagine for a moment that an unscrupulous blackguard of his type was going to lie down and accept your refusal? If you chose to refuse the money, so much the better for him; but whether you refused or accepted, he intended to suppress you. And but for me”⁠—he paused impressively⁠—“he would have done.”

Professor Goodman passed a bewildered hand across his forehead.

“But for me,” repeated Mr. Robinson, “you would now be dead⁠—foully murdered. You have never in your life⁠—and I trust you never will again⁠—been in such deadly peril as you were in a few days ago. Indeed, if it were known now that you were alive, I fear that even I would be powerless to save you.”

He drew carefully at his cigar; then he leaned forward and touched the Professor on the knee.

“Have you ever heard of a man called Peterson?”

“Never,” returned the other.

“No⁠—probably not. You and he hardly move in the same circles. Peterson, of course, is only one of the many names by which that arch-devil is known. He is a King of Criminals⁠—a man without mercy⁠—a black-hearted villain.” Mr. Robinson’s voice shook with the intensity of his emotion. “And to that man Sir Raymond Blantyre went with a certain proposal. Do you know what that proposal was? It concerned you and your death. You were to be murdered before you gave your secret to the world.”

“The villain!” cried Professor Goodman, in a shaking voice. “To think that I’ve had him to dinner, and that his wife is a friend of ours.”

Mr. Robinson smiled pityingly.

“My dear Professor,” he said, “I’m afraid that your life has been lived far apart from the realities of the world. Do you really suppose that such a trifle as that would have weighed for one instant with Sir Raymond Blantyre? However, I will get on with my explanation. It matters not how I discovered these things: I will merely say that for twenty years now I have dogged this man Peterson as his shadow. He did me the greatest wrong one man can do another: I won’t say any more.”

Mr. Robinson choked slightly.

“I have dogged him, Professor,” he went on after a while, “as I say, for twenty years, hoping⁠—always hoping⁠—that the time would come for my revenge. I have lived for nothing else; I have thought of nothing else. But one thing I was determined on⁠—that my revenge when it did come should be a worthy one. A dozen times could I have given him away to the police, but I stayed my hand. When it came, I wanted the thing to be more personal. And at last the opportunity did come. It came with you.”

“With me?” echoed Professor Goodman. “How can I have had anything to do with your revenge on this man?”

“That is what I am just going to explain to you,” continued Mr. Robinson. “In this man Peterson, Sir Raymond Blantyre had encountered a blackguard far more subtle than himself. Peterson was perfectly prepared to murder you⁠—but he had no intention of murdering the secret of your process. That he proposed to keep for himself⁠—so that he could continue blackmailing Sir Raymond. You see the manner of blackguard he is. It was a scheme after his own heart, and I made up my mind to strike at last. Apart from frustrating the monstrous crime of murdering you, I should achieve an artistic revenge.”

He again pulled thoughtfully at his cigar.

“Now pay close attention, Professor. Scheidstrun the German scientist made an appointment to see you, didn’t he?”

“He was with me when I was chloroformed,” cried the other.

Mr. Robinson smiled.

“No, he wasn’t. A man you thought was Scheidstrun was with you.”

“But⁠—good heavens!” gasped the Professor. “I met him in the hall. I was late, I remember⁠ ⁠…”

“And, as you say, you met him in the hall talking to your maidservant.”

“But how on earth did you know that?”

“Because the man you met in the hall was not Scheidstrun⁠—but me.” He laughed genially at the amazement on the other’s face. “It’s a shame to keep you mystified any further; I will explain everything. It was Peterson who made the original appointment with you, writing in Scheidstrun’s hand. What he intended to do I know not; how he intended to murder you I am not prepared to say. But the instant I discovered about it, I realised that there was not a moment to be lost. So I took the liberty, my dear Professor, of posing over the telephone as your secretary. I rang up Peterson, and speaking in an assumed voice I postponed his appointment with you until the following day. And then I took his place. I may say that I am not unskilled in the art of disguise, and I knew I could make myself up to resemble Scheidstrun quite sufficiently well to deceive you.”

“But why on earth didn’t you tell me at the time?” said Professor Goodman, peering at the speaker suspiciously.

Once again the other laughed.

“My dear fellow, surely Mrs. Goodman must, during the course of your married life, have let you into the secret of one of your characteristics. Or has she been too tactful? You are, as I think you must admit yourself, a little obstinate, aren’t you?” He dropped his tone of light banter, and became serious. “I don’t think⁠—in fact, I know you don’t realise the deadly peril you were in. Even had I succeeded in convincing you on the matter, and you had agreed to come away and hide yourself, you would not have consented to the destruction of your laboratory. And that was essential. As long as Peterson thought you were alive he would have found you wherever you had hidden yourself. It was therefore of vital importance that he should think you dead⁠—as he does now. Big issues, my dear Professor, require big treatments.”

Mr. Robinson, having delivered himself of this profound utterance, leaned back in his chair and gazed at his listener. Bland assurance radiated from his mutton-chop whiskers, but his mind was busy. How was the old fool taking it? He still had his trump card to play, but he wanted that to win the game without possibility of failure. And as his mental metaphors grew a little mixed, he realised that it must fall on carefully prepared soil.

Professor Goodman stirred uneasily in his chair.

“I really can hardly believe all this,” he said at length. “Why is all this deception necessary? Why have I to pose as your brother? And why, above all, have you tortured me?”

“Let me answer your last point first if I can,” said Mr. Robinson. “And yet I can’t. Even if I can persuade you to forgive me, I never shall be able to forgive myself. Sudden anger, Professor, makes men do strange things⁠—dreadful things. And I was furious with rage when I found that you had deliberately failed in the experiment. I realise now that I should have explained everything to you to start with. But I suppose my hatred of Peterson and my wish for revenge blinded me to other things. Everything, as I have told you, is subservient to that in my mind. Bringing you here, making you pose as my brother⁠—what was all that done for except to throw that devil off the scent should he by any chance suspect? And at present he does not. He believes that the secret for which he would have given untold gold has perished with you. He is angry, naturally, at what he considers a buffet of fate, but that is no use to me as a revenge. He must know that it was not fate⁠—but I who wrecked his scheme. He must know that not only has he lost the secret forever⁠—but that I have got it. There will be my revenge for which I have waited twenty years.” His eyes glistened, and he shook his fists in the air. “And then and not till then will it be safe for you to go back and join your wife.”

Professor Goodman leapt from his chair.

“You mean that?” he cried. “You will let me go?”

Mr. Robinson gazed at him in pained surprise; then he bowed his head.

“I deserve it,” he said in a low voice. “I deserve your bad opinion of me, firstly for not having told you, but especially for my vile and inexcusable loss of temper. But surely you can never have believed I was going to keep you here for good. Why”⁠—he gave a little pained laugh⁠—“it’s almost as if you thought I was a murderer. Foolish I may have been, obsessed with one idea, but I never thought that you would think quite as badly of me as that. After all, believe me or not as you like, I saved your life.”

He rose from his chair and paced thoughtfully up and down the room.

“No, no, my dear fellow⁠—please reassure yourself on that point. The very instant it is safe for you to do so, you shall return to your wife.”

“But when will it be safe?” cried the Professor excitedly.

“When Peterson knows that your secret is in my possession, and that therefore murdering you will avail him nothing,” answered Mr. Robinson calmly.

“But how do I know you will keep your word?”

“You don’t,” said the other frankly. “You’ve got to trust me. At the same time I beg of you to use your common sense. Of what possible advantage is it to me to keep you here? I shall have to trust you to take no steps to incriminate me, and that I am fully prepared to do. My quarrel is not with you, Professor; nor is it with that young man Drummond. But quite by accident he got between me and my life’s object⁠—and he had to be removed. So is it fair to Mrs. Goodman to keep her in this dreadful sorrow for one moment longer than is necessary? The very instant you have given me your secret, and your word of honour that you will say nothing to the police, you have my word of honour that you are free to go.”

“But what do you propose to do with my secret when you’ve got it?” asked the Professor. He was watching his captor with troubled eyes, wondering what to believe.

“Do with it?” cried the other exultantly. “I propose to seek out Peterson and let him know that I have got what he has missed. And if you but knew the man, you would realise that no more wonderful revenge could be thought of.”

“Yes, yes⁠—I see all that,” said the Professor irritably. “But in the event of my giving the secret to the world⁠—what then?”

Mr. Robinson curbed a rising desire to throttle the old man in the chair. Never had his self-control been so severely tried as it was now; precious moments were flying when every one was of value. But true to his new policy he kept every hint of irritation out of his voice as he answered.

“I shall have to have your promise also on that point, Professor. For one year you will have to keep your discovery to yourself. That will be sufficient for my revenge.”

He realised that had he made no proviso of that sort it would have been enough to raise the other’s suspicions, for Professor Goodman was no fool. He also realised that if he made the period too long the other’s inherent pigheadedness might tempt him to refuse. So he compromised on a year, and to his intense relief it looked as if the old man was inclined to consider it favourably. He still sat motionless, but his brow was wrinkled in thought, and he drummed incessantly with his fingers on the arms of his chair.

“One year,” he said at length. “For I warn you, sir, that all the Petersons in the world will not prevent me publishing my discovery then.”

“One year will be sufficient,” said Mr. Robinson quietly.

“And will you on your side,” continued the Professor, “promise not to publish it before that date?”

Mr. Robinson concealed a smile.

“I undoubtedly will promise that,” he answered.

“And the instant you possess the secret I may go to my wife?”

Mr. Robinson’s pulse was beating a little quicker than normal. Could it be that he had succeeded in bluffing him?

“As soon as Peterson knows that the secret of the process is mine⁠—and that will be very soon⁠—you may go. Before that it would not be safe.”

“And if I refuse?”

For a moment or two Mr. Robinson did not reply; he seemed to be weighing his words with care.

“Need we discuss that, Professor?” he said at length. “I have already told you the main⁠—almost the sole⁠—object of my life: revenge on this man Peterson. Rightly or wrongly, I have decided that this is my opportunity for obtaining it. I have gone to an immensity of trouble and risk to achieve my object, and though, as I said, I have no quarrel with you, yet, Professor, you are an essential part of my scheme. Without you I must fail; I make no bones about it. And I do not want to fail. So should you still refuse, your wife will go on thinking herself a widow until you change your mind. It rests with you and you alone.”

His eyes, shrewd and penetrating, searched the old man’s face. Had he said enough, or had he said too much? Like an open book he read the other’s mind: saw doubt, indecision, despair, succeed one another in rapid succession. And then suddenly he almost stopped breathing. For the Professor had risen to his feet, and Mr. Robinson knew that one way or the other he had come to a decision.

“Very well, sir,” said the old man wearily. “I give in. It seems that the only way of setting my poor wife’s mind at rest as soon as possible is for me to trust you. I will tell you my process.”

Mr. Robinson drew in his breath in a little whistling hiss, but his voice was quite steady as he answered.

“You have decided very wisely,” he remarked. “And since there is no time like the present, I think we will have a bottle of champagne and some sandwiches to fortify us, and then get on with the experiment at once.”

“As you will,” said the Professor. “And then perhaps tomorrow you will let me go.”

Mr. Robinson glanced at his watch.

“Today, Professor,” he remarked jovially. “It is past midnight. And I can promise you that should your experiment succeed, you will leave this house today.”

He watched the champagne bring back some colour to the other’s cheeks, and then he produced his notebook.

“To save time,” he said, “I propose to write down the name of each salt as you take it, and the amount you use. Does it make any difference in what order the salts are mixed?”

“None whatever,” answered the Professor. “Provided they are all mixed properly. No chemical reaction takes place until the heat is applied.”

“And to make it perfectly certain, you had better give me the formula for each salt at the same time,” continued Mr. Robinson.

At first the old man’s fingers trembled so much that he could hardly use the balance, but Mr. Robinson betrayed no impatience. And after a while the enthusiasm of the scientist supplanted everything else, and the Professor became absorbed in his task. Entry after entry was made in Mr. Robinson’s neat handwriting, and gradually the look of triumph deepened in his eyes. Success had come at last.

Of pity for the poor old man opposite he felt no trace; pity was a word unknown in his vocabulary. And so for an hour in the silent house the murderer and his victim worked on steadily, until, at length, the last salt was mixed, the last entry made. The secret was in Mr. Robinson’s possession. Not for another four hours would he be absolutely certain; the test of the electric furnace would furnish the only conclusive proof. But short of that he felt as sure as a man may feel that there had been no mistake this time, and his eyes were gleaming as he rose from the table.

“Excellent, my dear Professor,” he murmured. “You have been lucidity itself. Now all that remains is to start up our current and await results.”

“The results will be there,” answered the other. “That I know.”

He opened the furnace door and placed the retort inside; then, switching on the current, he sank wearily into his chair.

“You don’t think it will be long, do you, before you can convince this man Peterson?” he said with a pathetic sort of eagerness.

“I can assure you that it won’t be,” returned the other, with an enigmatic smile. “I keep in very close touch with him.”

“Because I would be prepared to run any risk in order to let my dear wife know that I am alive as soon as possible.”

Mr. Robinson nodded sympathetically.

“Of course you would, my dear fellow. I quite understand that. But I feel that I must safeguard you even against your own inclinations. The instant, however, that I consider it safe, you shall go back.”

“Can’t I even write to her?” queried the other.

Mr. Robinson affected to consider the point, then regretfully he shook his head.

“No⁠—not even that,” he answered. “I know this man Peterson too well. In fact, Professor, I am not even going to allow you to return to your wife from this house. It is better and safer for you that you should remain in ignorance of where you have been, and so I propose to take you for a short sea-voyage in my yacht and land you on another part of the coast. From the boat you will be able to radio to your wife, so that her mind will be set at rest. And then when you finally rejoin her, I would suggest your pleading sudden loss of memory to account for your mysterious disappearance.”

“But what on earth am I to say about the man who was buried?” And suddenly the full realisation of all that the question implied came home to him and he stood up. “Who was that man?”

“An uninteresting fellow,” remarked Mr. Robinson genially.

“But if you were the man I thought was Scheidstrun, you must⁠—you must have murdered him.” The old man’s voice rose almost to a scream. “My God! I’d forgotten all about that.”

He shrank back staring at Mr. Robinson, who was watching him narrowly.

“My dear Professor,” he said coldly, “pray do not excite yourself unnecessarily. I have often thought that a society of murderers run on sound conservative lines would prove an admirable institution. After all, it is the majority who should be considered, and there are so many people who are better out of the way. However, to set your mind at rest,” he continued, “it may interest you to know that the foot which was buried in your boot did not belong to a living man. There are methods of obtaining these things, as you are doubtless aware, for experimental purposes, if you possess a degree.”

There was no object, he reflected, in unnecessarily alarming the old man; it saves bother to get an animal to walk to the slaughterhouse rather than having to drag it there. And he was likely to have all the dragging he wanted with Drummond, even though he was insane.

Professor Goodman, only half satisfied, sank back in his chair. Already the sweat was running down both their faces from the heat of the furnace, but Mr. Robinson had no intention of leaving the room. He was taking no chances this time; not until the current was turned off and the furnace was cool enough to handle did he propose to go and rest. Then, once he was satisfied that the retort did contain diamonds, he would have some badly needed sleep in preparation for the work next night.

The yacht Gadfly was lying in Southampton Water, and he had decided to go on board in the late afternoon. His two invalids would be carried on stretchers; an ambulance was even now in readiness below to take them to the coast. They would both be unconscious⁠—a matter which presented but little difficulty to Mr. Robinson. And the Professor would never regain consciousness. He had served his purpose, and all that mattered as far as he was concerned was to dispose of him as expeditiously as possible. With Drummond things were a little different. In spite of what he had said to Freyder downstairs, the scheme was too big to run any unnecessary risks, and though it went against his grain to kill him in his present condition, he quite saw that he might have to. Drummond might remain in his present condition for months, and it was manifestly impossible to wait for that length of time to obtain his revenge. It might be, of course, that when he woke up he would have recovered his reason, and, if so⁠ ⁠… Mr. Robinson’s eyes gleamed at the thought. In anticipation he lived through the minute when he would watch Drummond, bound and weighted, slip off the deck into the sea.

Then with an effort he came back to the present. Was there anything left undone in his plans which would cause a check? Point by point he ran over them, and point by point he found them good. Their strength lay in their simplicity, and he could see nothing which was likely to go wrong before he was on board the Gadfly. Up to date no mention of Mr. Lewisham’s sudden disappearance had found its way into the papers; presumably, whatever Mrs. Lewisham might think of the matter, she had not consulted the police. Similarly with regard to Drummond. No questions were likely to be asked in his case until long after he was safely out of the country. And after that, as he had said to Freyder, nothing mattered. The S.Y. Gadfly would founder with all hands somewhere off the coast of Africa, but not too far from the shore to prevent Freyder and himself reaching it. That the crew, drugged and helpless, would go down in her he did not propose to tell them when he went on board. After all, there were not many of them, and it would be a pity to spoil their last voyage.

The heat from the furnace was growing almost insupportable, and he glanced at his watch. There was another hour to go, and with a sigh of impatience he sat back in his chair. Opposite him Professor Goodman was nodding in a kind of heavy doze, though every now and then he sat up with a jerk and stared about him with frightened eyes. He was muttering to himself, and once he sprang out of his chair with a stifled scream, only to sink back again as he saw the motionless figure opposite.

“I was dreaming,” he muttered foolishly. “I thought I saw a man standing by the door.”

Mr. Robinson swung round and peered into the passage; there was no one there. Absolute silence still reigned in the house. And then suddenly he rose and went to the door: it seemed to him as if something had stirred outside. But the passage was empty, and he resumed his seat. He felt angry with himself because his own nerves were not quite under their usual iron control. After all, what could possibly happen? It must be the strain of the last few days, he decided.

Slowly the minutes ticked on, and had anyone been there to see, it must have seemed like some ceremony of black magic. The furnace glowing white hot, and in the circle of light thrown by it two elderly men sitting in chairs⁠—one gently stroking his mutton-chop whiskers, the other muttering restlessly to himself. And then outside the ring of light⁠—darkness. Every now and then a sizzling hiss came from inside the furnace, as the chemical process advanced another stage towards completion⁠—that completion which meant all power to one of the two who watched and waited, and death to the other. The sweat dripped down their faces; breathing was hard in the dried-up air. But to Mr. Robinson nothing mattered: such things were trifles. Whatever might be the material discomfort, it was the crowning moment of his life⁠—the moment when the greatest coup of his career had come to a successful conclusion.

And suddenly he shut his watch with a snap.

“Two hours,” he cried, and strive as he would he could not keep the exultation out of his voice. “The time is up.”

With a start Professor Goodman scrambled to his feet, and mumbling foolishly he switched off the current. It was over; he had given away his secret. And all he wanted to do now was to get home as soon as possible. Two hours more to let it cool⁠ ⁠…

He paused, motionless, his lips twitching. Great heavens! what was that in the door⁠—that great dark shape. It was moving, and he screamed. It was coming into the circle of light, and as he screamed again, Mr. Robinson leapt to his feet.

Once more the thing moved, and now the light from the furnace shone on it. It was Drummond, his arms still lashed in front of him. His face was covered with blood, but his eyes were fixed on Professor Goodman. And they were the eyes of a homicidal maniac.

For a moment or two Mr. Robinson stood motionless, staring at him. Drummond’s appearance was so utterly unexpected and terrifying that his brain refused to work, and before he realised what had happened, Drummond sprang. But not at him. It was Professor Goodman who had evidently incurred the madman’s wrath, and the reason was soon obvious. Insane though he was, the one dominant idea of his life was still a ruling factor in his actions, though now it was uncontrolled by any reason. And that idea was Peterson.

Why he should imagine that Professor Goodman was Peterson it was impossible to say, but he undoubtedly did. Again and again he grunted the name as he shook the unfortunate scientist backwards and forwards, and for a while Mr. Robinson wondered cynically whether he should let him go on in his delusion and await results. He was almost certain to kill the old man, which might save trouble. At the same time there was still the possibility of some mistake in the process, which rendered it inadvisable to dispense with him for good quite yet.

An uproar in the passage outside took him to the door. Two of the three men who had been told off to guard Drummond were running towards him, and he cursed them savagely.

“Pull him off,” he roared. “He’ll murder the old man.”

They hurled themselves on Drummond, who had forced the Professor to his knees. And this time, strangely enough, he gave no trouble. He looked at them with a vacant stare, and then grinned placidly.

“Chief!” cried one of the men, “he’s murdered Simpson. He’s lying there with his neck broken.”

Mr. Robinson darted from the room, to return almost at once. It was only too true. The third man was lying across the bed dead.

“Where were you two imbeciles?” he snarled savagely.

“We were taking it in turns, boss,” said the one who had spoken, sullenly. “The swine was asleep and his arms were bound⁠ ⁠…”

He turned vindictively on Drummond, who grinned vacantly again.

“So you left him alone with only one of you,” Mr. Robinson remarked coldly. “You fools!⁠—you triple-distilled damned fools. And then I suppose he woke and Simpson went to tuck him up. And Drummond just took him by the throat, and killed him, as he’d kill you or anyone else he got his hands on⁠—bound or not.”

“Gug-gug,” said Drummond, sitting down and beaming at them. “That man in there hit me in the face, when I took his throat in my hands.”

And suddenly the madness returned to his eyes, and his huge hands strained and wrestled with the rope that bound them. He grunted and cursed, and the two men instinctively backed away. Only Mr. Robinson remained where he was, and the light from the still glowing furnace glinted on the revolver which he held in his hand. This was no time for half-measures; there was no telling what this powerful madman might do next. If necessary, though he did not want to have to do it, he would shoot him where he sat. But the spasm passed, and he lowered his revolver.

“Just so,” he remarked. “You might as well hit a steamroller as hit Drummond, once he’s got hold. And judging by his face, Simpson must have hit him hard and often before he died. Take him away; lash him up; and unless you want to join that fool Simpson, don’t take it in turns to guard him⁠—and don’t get within range of his hands.”

The two men closed in warily on their prisoner, but he gave no further bother. Babbling happily he walked between them out of the room, and Mr. Robinson suddenly remembered the unfortunate Professor.

“A powerful and dangerous young man,” he remarked suavely. “I trust he hasn’t hurt you, my dear Professor.”

“No,” said the other dazedly; “he hasn’t hurt me.”

“An extraordinary delusion of his,” pursued Mr. Robinson. “Fancy thinking that you, of all people, were that villain Peterson.”

“Most extraordinary!” muttered the Professor.

“And it’s really quite amazing that he should have allowed himself to be separated from you so easily. His friends, I believe, call him Bulldog, and he has many of the attributes of that noble animal.” He peered at the Professor’s throat. “Why, he’s hardly marked you. You can count yourself very lucky, believe me. Even when sane he’s a terror⁠—but in his present condition⁠ ⁠… However, such a regrettable contretemps will not occur again, I trust.”

He glanced at the furnace.

“Another hour, I suppose, before it will be cool enough to see the result of our experiment?”

“Another hour,” agreed the Professor mechanically.

And during that hour the two men sat in silence. Each was busy with his own thoughts, and it would be hard to say which would have received the greater shock had he been able to read the other’s mind.

For Mr. Robinson was thinking, amongst other things, of the approaching death of the Professor, which would scarcely have been comforting to the principal actor in the performance. And Professor Goodman⁠—who might have been expected to be thinking of nothing but his approaching reunion with his wife⁠—had, sad to relate, completely forgotten the lady’s existence. His mind was engrossed with something quite different. For when a man who is undoubtedly mad⁠—so mad, in fact, that in a fit of homicidal mania he has just throttled a man⁠—gets you by the throat, you expect to experience a certain discomfort. But you do not expect to be pushed backwards and forwards as a child is pushed when you play with it⁠—without discomfort or hurt. And above all you do not expect that madman to mutter urgently in your ear, “For God’s sake⁠—don’t give your secret away. Delay him⁠—at all costs. You’re in the most deadly peril. Burn the house down. Do anything.”

Unless, of course, the madman was not mad.