Venner lost no time in reaching the rooms of his friend Gurdon, and was fortunate enough to find the latter at home. He was hard at work on some literary matter, but he pushed his manuscript aside as Venner came excitedly into the room.

"Well, what is it?" he asked. "Anything fresh? But your face answers that question. Have you found Bates?"

"No, I haven't," Venner said; "but he seems to have been discovered. I bought this paper just now in Piccadilly, but I have not been able to look at it yet. It is stated here that the mystery has been solved."

"Hand it over," Gurdon cried excitedly. "Let's see if we can find it. Ah! here we are. The Press Association has just received a letter which appears to come from Mr. Bates himself. He says he is very much annoyed at all this fuss and bother in the papers, about his so-called kidnapping. He goes on to say that he was called to the Continent by pressing business, and that he had not even time to tell his servants he was going, as it was imperatively necessary that he should catch the midnight boat to Dieppe. The correspondent of the Press Association says that Mr. Bates has been interviewed by a foreign journalist, who is absolutely certain as to his identity. Moreover, an official has called at Mr. Bates' residence and found that his servants have had a letter from their master instructing them to join him at once, as he has let his house furnished for the next two months. Well, my dear man, that seems to be very satisfactory, and effectually disposes of the idea that Mr. Bates has been mysteriously kidnapped. I am rather sorry for this in a way, because it upsets all our theories and makes it necessary to begin our task all over again."

"I don't believe a word of it," Venner said. "I believe it's a gigantic bluff. I was coming to see you to-night in any case, but after buying that paper I came on here post haste. Now that story of the Press Association strikes me as being decidedly thin. Here is a man living comfortably at home who suddenly disappears in a most mysterious manner, and nothing is heard of him for some time. Directly the public began to regard it as a fascinating mystery and the miscreants realising what a storm they were likely to stir up, the man himself writes and says that it is all a mistake. Now, if he had come back and shown himself, it would have been quite another matter. Instead of doing that, he writes a letter from abroad, or sends a telegram or something of that kind, saying that he has been called away on urgent business. That might pass easily enough, but mark what follows. He writes to his servants asking them to join him at once in some foreign town because he has let his house for two months, and the new tenant wishes to get in without delay. Did ever anybody hear anything so preposterous? Just as if a man would let a house in that break-neck fashion without giving his servants due warning. The thing is not to be thought of."

"Then you think the servants have been lured away on a fools' errand?"
Gurdon asked. "You don't think there is anybody in the house?"

"Oh, yes, I do," Venner said drily. "I have a very strong opinion that there are people in the house, and I also have a pretty shrewd idea as to who they are. It happens, also, that I am in a position to test my theory without delay."

"How do you propose to do that?" Gurdon asked.

"Quite easily. After I left you this afternoon I went back to the agent and succeeded in obtaining possession of the keys of the empty house in Portsmouth Square. My excuse was that I wanted to go into detail and to take measurements and the like. I need not remind you that Bates' house is next door to the empty one. In fact, there is no question that both houses belong to the same person. You will remember, also, the mysterious way in which that furniture vanished from the scene of your adventure."

"I remember," Gurdon said grimly. "But all the same I don't quite see what you are driving at."

"The thing is quite plain. That furniture did not vanish through the prosaic medium of a van, nor was it carted through the front door from one house to the other. The two houses communicated in some way, and it will be our business to find the door. As I have the keys and every legitimate excuse for being on the premises, we can proceed to make our investigations without the slightest secrecy, and without the least fear of awkward questions being asked. Now do you follow me?"

"I follow you fast enough. I suppose your game is to try and get into the next house by means of the door?"

"You have hit it exactly," Venner said. "That is precisely what I mean to do. We shall find it necessary to discover the identity of Mr. Bates' tenant."

"When are we going to make the experiment?" Gurdon asked.

"We are going to make it now," Venner replied. "We will have a cab as far as the Empire Hotel, so that I can get the keys. After that, the thing will be quite easy. Come along, and thank me for an exciting evening's adventure. I shall be greatly surprised if it is not even more exciting than the last occasion."

They were in the empty house at last. The windows were closed and shuttered, so that it was possible to use matches in the various rooms without attracting attention from the outside. But search how they would, for upwards of two hours, they could find no trace whatever of a means of communication between the two houses. They tapped the walls and sounded the skirtings, but without success. Venner paced the floor of the drawing-room moodily, racking his brains to discover a way out of the difficulty.

"It must be here somewhere," he muttered. "I am sure all that furniture was moved backwards and forwards through some door, and a wide one at that."

"Then it must be on the ground floor," Gurdon remarked. "When you come to think of it, some of that furniture was so heavy and massive that it would not go through an ordinary doorway, neither could it have been brought upstairs without the assistance of two or three men of great strength. We shall have to look for it in the hall; if we don't find it there, we shall have to give it up as a bad job and try some other plan."

"I am inclined to think you are right," Venner said. "Let us go down and see. At any rate, there is one consolation. If we fail to-night we can come again to-morrow."

Gurdon did not appear to be listening. He strode resolutely down the stairs into the hall and stood for some moments contemplating the panels before him. The panels were painted white; they were elaborately ornamented with wreaths of flowers after the Adams' style of decoration. Then it seemed to Gurdon that two pairs of panels, one above and one below, had at one time taken the formation of a doorway. He tapped on one of the panels, and the drumming of his fingers gave out a hollow sound. Gurdon tapped again on the next panel, but hardly any sound came in response. He looked triumphantly at Venner.

"I think we have got it at last," he said. "Do you happen to have a knife in your pocket? Unless I am greatly mistaken, the decorations around these panels come off like a bead. If you have a knife with you we can soon find out."

Venner produced a small knife from his pocket, and Gurdon attempted to insinuate the point of the blade under the elaborate moulding. Surely enough, the moulding yielded, and presently came away in Gurdon's hands.

"There you are," he said. "It is exactly as I told you. I thought at first that those mouldings were plaster, but you can see for yourself now that they are elaborately carved wood."

Venner laid the ornament aside and stood watching Gurdon with breathless interest while the latter attacked another of the mouldings. They came away quite easily, pointing to the fact that they must have been removed before within a very short period. Once they were all cleared away, Gurdon placed the point of the knife behind one of the panels, and it came away in his hands, disclosing beyond a square hole quite large enough for anybody to enter. Here was the whole secret exposed.

"Exactly what I thought," Gurdon said. "If I removed all the mouldings from the other three panels there would be space enough here to drive a trap through. I think we have been exceedingly lucky to get to the bottom of this. How clever and ingeniously the whole thing has been managed! However, I don't think there is any occasion for us to worry about moving any more of the panels, seeing that we can get through now quite easily. Wouldn't it be just as well to put all the lights out?"

"I haven't thought of that," Venner muttered. "On the whole, it would be exceedingly injudicious not to extinguish all the lights. We had better go on at once, I think, and get it over."

The house was reduced to darkness, and very quietly and cautiously the two adventurers crept through the panel. They were in the hall on the other side, of which fact there was no doubt, for they stepped at once off a marble floor on to a thick rug which deadened the sound of their footsteps. They had, naturally enough, expected to find the whole place in darkness, and the tenant of the house and his servants in bed. This, on the whole, would be in their favor, for it would enable them to take all the observations they required with a minimum chance of being disturbed.

A surprise awaited them from the first. True, the hall was in darkness, and, as far as they could judge, so was the rest of the house. But from somewhere upstairs came the unmistakable sound of a piano, and of somebody singing in a sweet but plaintive soprano voice. Gurdon clutched his companion by the arm.

"Don't you think it is just possible that we have made a mistake?" he whispered. "Isn't it quite on the cards that this is a genuine affair, and that we are intruding in an unwarrantable manner upon some respectable private citizen? I am bound to say that that beautiful voice does not suggest crime to me."

"We must go on now," Venner said, impatiently. "It won't do to judge by appearances. Let us go up the stairs and see what is going on for ourselves. If we are intruding, we will get away as speedily as possible."

Gurdon made no further objection, and together they crept up the stairs. There was no chance of their being surprised from behind by the servants, for they had taken good care to notice that the basement was all in darkness. They were getting nearer and nearer now to the sound of the music, which appeared to come from the drawing-room, the door of which was widely enough open for the brilliant light inside to illuminate the staircase. A moment later the music ceased, and someone was heard to applaud in a hoarse voice.

"Sing some more," the voice said. "Now don't be foolish, don't begin to cry again. Confound the girl, she makes me miserable."

"Do you recognise the voice?" Venner whispered.

"Lord! yes," was Gurdon's reply. "Why, it's Fenwick. No mistaking those tones anywhere. Now, what on earth does all this mean?"

"We shall find out presently," Venner said. "You may laugh at me, but I quite expected something of this kind, which was one of the reasons why I obtained the keys of the house."

"It's a most extraordinary thing," Gurdon replied. "Now isn't this man—Fenwick—one of the last persons in the world you would credit with a love of music?"

"I don't know," Venner said. "You never can tell. But don't let's talk. We are here more to listen than anything else. I wish we could get a glimpse of the singer."

"I am going to," Gurdon declared. "Unless I am greatly mistaken, I have made a discovery, too. Oh, I am not going to take any risk. Do you see that mirror opposite the door? It strikes me if I get close enough to look into it that I shall be able to see who is in the room without betraying my presence."

So saying, Gurdon crept forward till he was close enough to the mirror to get a very good idea of the room and its occupants. He could see a pale figure in white standing by a piano; he could see that Fenwick was sprawling in a big armchair, smoking a large cigar. Then he noticed that the girl crossed the floor and laid a slim hand half timidly, half imploringly, on Fenwick's shoulder.

"Why are you so unkind to me?" she said. "Why so cruel? How many times have you promised me that you will bring him back to me again? I get so tired of waiting, I feel so sad and weary, and at times my mind seems to go altogether."

"Have patience," Fenwick said. "If you will only wait a little longer he will come back to you right enough. Now go to the piano and sing me another song before I go to bed. Do you hear what I say?"

The last words were harshly uttered; the girl reeled back as if fearing a blow. Gurdon standing there clenched his fists impulsively; he had considerable difficulty in restraining himself.

"Very well," she said; "just one more, and then I will go to bed, for I am so tired and weary."

Once more the sweet pathetic voice rang out in some simple song; the words gradually died away, and there was silence. Gurdon had barely time to slip back to the head of the stairs before the girl came out and made her way to the landing above. Standing just below the level of the floor, Venner gazed eagerly at the pretty tired face and mournful blue eyes. He grasped his companion by the arm in a grip that was almost painful.

"We are getting to it," he said. "It was a good night's work coming here to-night. Do you mean to say you don't notice the likeness? Making due allowance for the difference in height and temperament, that poor girl is the image of my wife."

"I must have been a dolt not to have noticed it before," Gurdon said. "Now that you mention it, the likeness is plain enough. My dear fellow, can't you see in this a reason for your wife's reticence in speaking of the past?"

There was no time to reply, for the sinister evil face of Fenwick appeared in the doorway, and he called aloud in Spanish some hoarse command, which was answered from above by someone, in the same language. Gurdon whispered to his companion, with a view to ascertaining what had been said.

"You will see for yourself in a minute," Venner said in an excited whisper. "You are going to have another surprise. You wanted to know just now what had become of Bates. Unless I am greatly mistaken, you will be able to judge for yourself in a few moments. I believe the man to be a prisoner in his own house."