T. B. Smith's inspection of the Secret House had yielded nothing satisfactory; he had not expected that it would; he was perfectly satisfied that the keen, shrewd brains which dominated the menage would remove any trace there was of foul play.

"Where now?" asked Ela, as they turned out of the house.

"Back to Moor Cottage," said T. B., climbing into the car. "I am certain that we are on the verge of our big discovery. There is a way out of the cottage by some underground chamber, a way by which first Lady Constance and then Poltavo were smuggled, and if it is necessary I am going to smash every panel in those two ground floor rooms, but I will find the way in to Mr. Farrington's mystery house."

For half an hour the two men were engaged in the room from which Poltavo had been taken. They probed with centre bits and gimlets into every portion of the room.

The first discovery that they made was that the oaken panels of the chamber were backed with sheet iron or steel.

"It is a hopeless job; we shall have to get another kind of smith here to tear down all the panellings," said T. B., lighting the gloom of his despair with a little flash of humour.

He fingered the tiny locket absently and opened it again.

"It is absurd," he laughed helplessly. "Here is the solution in these simple words, and yet we brainy folk from the Yard cannot understand them!"

"God sav the Keng!" said Ela ruefully. "I wonder how on earth that is going to help us."

A gasp from T. B. made him turn his face to his chief.

T. B. Smith was pointing at the piano. In two strides he was across the room, and sitting on the stool he lifted the cover and struck a chord. The instrument sounded a little flat and apparently had not received the attention of a tuner for some time.

"I am going to play 'God save the King,'" said T. B. with a light in his eyes, "and I think something is going to happen."

Slowly he pounded forth the familiar tune; from beginning to end he played it, and when he had finished he looked at Ela.

"Try it in another key," suggested Ela, and again T. B. played the anthem. He was nearing the last few bars when there was a click and he leapt up. One long panel had disappeared from the side of the wall. For a moment the two men looked at one another. They were alone in the house, although a policeman was within call. The main force was gathered in the vicinity of the Secret House.

T. B. flashed the light of his indispensable and inseparable little electric lamp into the dark interior.

"I will go in first and see what happens," he said.

"I think we will both go together," said Ela grimly.

"There is a switch here," said T. B.

He pulled it down and a small lamp glowed, illuminating a tiny lift cage.

"And here I presume are the necessary controlling buttons," said T. B., pointing to a number of white discs; "we will try this one."

He pressed the button and instantly the cage began to fall. It came to a standstill after a while and the men stepped out.

"Part of the old working," said T. B.; "a very ingenious idea."

He flashed his lamp over the walls to find the electrical connection. They were here, as they were at the other end, perfectly accessible. An instant later the long corridor was lighted up.

"By heavens," said T. B. admiringly, "they have even got an underground tramway; look here!"

At this tiny terminus there were two branches of rails and a car was in waiting. A few minutes later T. B. Smith had reached the other end of the mine gallery and was seeking the second elevator.

"Here we are," he said—"everything run by electricity. I thought that power house of Farrington's had a pretty stiff job, and now I see how heavy is the load which it has to carry. Step carefully into this," he continued, "and make a careful note of the way we are going. I think we must be about a hundred feet below the level of the earth; just gauge it roughly as we go up. Here we go."

He pressed a button and up went the lift. They passed out of the little mine chamber, carefully propping back the swing door, and made their way along the corridor.

"This looks like an apartment," said T. B., as he stopped before a red-painted steel door in one of the walls. He pressed it gently, but it did not yield. He made a further examination, but there was no keyhole visible.

"This is either worked by a hidden spring or it does not work at all," he said in a low voice.

"If it is a spring," said Ela, "I will find it."

His sensitive hands went up and down the surface of the door and presently they stopped.

"There is something which is little larger than a pin hole," he said. He took from his pocket a general utility knife and slipped out a thin steel needle. "Pipe cleaners may be very useful," he said, and pressed the long slender bodkin into the aperture. Instantly, and without sound, the door opened.

T. B. was the first to go in, revolver in hand. He found himself in a room which, even if it were a prison, was a well-disguised prison. The walls were hung with costly tapestry, the carpet under foot was thick and velvety and the furniture which garnished the room was of a most costly and luxurious description.

"Lady Constance!" gasped T. B. in surprise.

A woman who was sitting in a chair near the reading lamp rose quickly and turned her startled gaze to the detective.

"Mr. Smith," she said, and ran towards him. "Oh, thank God you have come!"

She grasped him by his two arms; she was half hysterical in that moment of her release, and was babbling an incoherent string of words; a description of her capture—her fear—her gratitude—all in an inextricably confused rush of half completed phrases.

"Sit down, Lady Constance," said T. B. gently; "collect yourself and try to remember—have you seen Poltavo?"

"Poltavo?" she said, startled into coherence. "No, is he here?"

"He is somewhere here," said T. B. "I am seeking for him now. Will you stay here or will you come with us?"

"I would rather come with you," she said with a shiver.

They passed through the door together.

"Do all these doors open upon rooms similar to this?" asked T. B.

"I believe there are a number of underground cells," she answered in a whisper, "but the principal one is that which is near." She pointed to a red-painted door some twenty paces away from the one from which they were emerging. There was another pause whilst Ela repeated his examination of the door.

Apparently they all worked on the pick system, a method which medieval conspirators favoured, and which the Italian workmen probably imported from the land of their birth; a land which has given the world the Borgias and the Medicis and the Visconti.

"Stay here," said T. B. in a low voice, and Lady Constance shrank back against the wall.

Ela pressed in his little needle and again the result was satisfactory. The door opened slowly and T. B. stepped in.

He stood for a moment trying to understand all that the terrible scene signified. The limp body on the floor; the two remorseless men standing close by; Farrington with folded arms and his eye glowering down upon the dead man at his feet. Fall at the switchboard.

Then T. B.'s revolver rose swiftly.

"Hands up!" he said.

The words were hardly out of his mouth when the room was plunged in darkness, his companion was flung violently backward as the electrical control came into operation and the door slammed in Ela's face. He pressed it without avail. He brought to his aid the little needle, but this time the lock would not move.

Ela's face went chalk white.

"My God!" he gasped, "they've got T. B.!"

He stood for a moment in indecision. He had visualized the scene and knew what fate would befall his chief.

"Back to the gallery," he said harshly, and led the way, holding the woman's arm in support. He found his way without difficulty to the lift, sprang into it, after Lady Constance, and pressed the button.... Now they were speeding along the sparking rail ... now they were in the lift rising swiftly to the room in Moor Cottage. T. B.'s car was outside.

"You had better come with me," said Ela quickly.

Lady Constance jumped into the car after him.

"To the Secret House," said Ela to the chauffeur, and as the car drove forward he turned to the woman at his side.

"I will put you amongst your friends in a few moments," he said; "at present I dare not risk the loss of a second."

"But what will they do?"

"I pretty well know what they will do," said Ela grimly. "Farrington is playing his last hand, and T. B. Smith is to be his last victim."

In the darkness of the underground chamber T. B. faced his enemies, striving to pierce the gloom, his finger in position upon the delicate trigger of his automatic pistol.

"Do not move," he said softly; "I will shoot without any hesitation."

"There is no need to shoot," said the suave voice of the doctor; "the lights went out, quite by accident, I assure you, and you and your friends have no need to fear."

T. B. groped his way along the wall, his revolver extended. In the gloom he felt rather than saw the bulky figure of the doctor and reached out his hand gingerly.

Then something touched the outstretched palm, something that in ordinary circumstances might have felt like the rough points of a bass broom. T. B. was flung violently backwards and fell heavily to the ground.

"Get him into the chair quick," he heard Farrington's voice say. "That was a good idea of yours, doctor."

"Just a sprayed wire," said Dr. Fall complacently; "it is a pretty useful check upon a man. You took a wonderful assistant when you pressed electricity to your aid, Farrington."

The lights were all on now, and T. B. was being strapped to the chair. He had recovered from the shock, but he had recovered too late. In the interval of his unconsciousness the body of Poltavo had been removed out of his sight. They were doing to him all that they had done to Poltavo. He felt the electrodes at his calf and on his wrists and clenched his teeth, for he knew in what desperate strait he was.

"Well, Mr. Smith," said Farrington pleasantly, "I am afraid you have got yourself into rather a mess. Where is the other man?" he asked quickly. He looked at Fall, and the doctor returned his gaze.

"I forgot the other man," said Fall slowly; "in the corridor outside." He went to the invisible door and it opened at his touch. He was out of the room a few minutes, and returned looking old and drawn.

"He has got away," he said; "the woman has gone too."

Farrington nodded.

"What does he matter?" he asked roughly; "they know as much as they are likely to know. Put the control on the door."

Fall turned over a switch and the other renewed his attention to T. B.

"You know exactly how you are situated, Mr. Smith," said Farrington, "and now I am going to tell you exactly how you may escape from your position."

"I shall be interested to learn," said T. B. coolly, "but I warn you before you tell me that if my escape is contingent upon your own, then I am afraid I am doomed to dissolution."

The other nodded.

"As you surmise," he said, "your escape is indeed contingent upon mine and that of my friends. My terms to you are that you shall pass me out of England. I know you are going to tell me that you have not the power, but I am as well acquainted with the extraordinary privileges of your department as you are. I know that you can take me out of the Secret House and land me in Calais to-morrow morning, and there is not one man throughout the length and breadth of England who will say you nay. I offer you your life on condition that you do this, otherwise——"

"Otherwise?" asked T. B.

"Otherwise I shall kill you," said Farrington briefly, "just as I killed Poltavo. You are the worst enemy I have and the most dangerous. I have always marked you down as one whose attention was to be avoided, and I shall probably kill you with less compunction because I know that but for you I should not have been forced to live this mad dog's life that has been mine for the past few months. You will be interested, Mr. Smith, to learn that you nearly had me once. You see the whole wing of the house in which Mr. Moole lies," he smiled, "works on the principle of a huge elevator. The secret of the Secret House is really the secret of perfectly arranged lifts; that is to say," he went on, "I can take my room to the first floor and I can transport it to the fourth floor with greater ease than you can carry a chair from a basement to an attic."

"I guessed that much," said T. B. "Do you realize that you might have made a fortune as a practical electrician?"

Farrington smiled.

"I very much doubt it," he said coolly; "but my career and my wasted opportunities are of less interest to me at the moment than my future and yours. What are you going to do?"

T. B. smiled.

"I am going to do nothing," he said cheerfully, "unless it be that I am going to die, for I can imagine no circumstance or danger that threatens me or those I love best which would induce me to loose upon the world such dangerous criminals as yourself and your fellow-murderers. Your time has come, Farrington. Whether my time comes a little sooner or later does not alter the fact that you are within a month of your own death, whether you kill me or whether you let me go."

"You are a bold man to tell me that," said Farrington between his teeth.

T. B. saw from a glance at the blanched faces of the men that his words had struck home.

"If you imagine you can escape," T. B. went on unconcernedly, "why, I think you are wasting valuable time which might be better utilized, for every moment of delay is a moment nearer to the gallows for both of you."

"My friend, you are urging your own death," said Fall.

"As to that," said T. B., shrugging his shoulders, "I have no means of foretelling, because I cannot look into the future any more than you, and if it is the will of Providence that I should die in the execution of my duty, I am as content to do so as any soldier upon the battle-field, for it seems to me," he continued half to himself, "that the arrayed enemies of society are more terrible, more formidable, and more dangerous than the massed enemies that a soldier is called upon to confront. They are only enemies for a period; for a time of madness which is called 'war'; but you in your lives are enemies to society for all time."

Fall exchanged glances with his superior, and Farrington nodded.

The doctor leant down and picked up the leather helmet, and placed it with the same tender care that he had displayed before over the head of his previous victim.

"I give you three minutes to decide," said Farrington.

"You are wasting three minutes," said the muffled voice of T. B. from under the helmet.

Nevertheless Farrington took out his watch and held it in his unshaking palm; for the space of a hundred and eighty seconds there was no sound in the room save the loud ticking of the watch.

At the end of that time he replaced it in his pocket.

"Will you agree to do as I ask?" he said.

"No," was the reply with undiminished vigour.

"Let him have it," said Farrington savagely.

Dr. Fall put up his hand to the switch, and as he did so the lights flickered for a moment and slowly their brilliancy diminished.

"Quick," said Farrington, and the doctor brought the switch over just as the lights went out.

T. B. felt a sharp burning sensation that thrilled his whole being and then lost consciousness.