'The impossible situation? No, but I have a clear course now to tell you the whole story from the beginning.'

'Yes, but let me get this straightened out. If Grimaud, as you say, shot Fley in Cagliostro Street just before nine - forty - five -'

'I didn't say that,' said Dr Fell.

'What?'

'You'll understand if you follow my patient elucidation from the beginning. On Wednesday night of last week - when Fley first appeared out of the past, apparently out of his grave to confront his brother with rather a terrible threat at the Warwick Tavern - Grimaud resolved to kill him. In the whole case, you see, Grimaud was the only person with a motive for killing Fley. And, my G.o.d! Hadley, but he did have a motive! He was safe, he was rich, he was respected; the past buried. And then, all of a sudden, a door blows open to admit this thin grinning stranger who is his brother Pierre. Grimaud, in escaping from prison, had murdered one of his brothers by leaving him buried alive; he would have murdered the other except for an accident. He could still be extradited and hanged - and Pierre Fley had traced him.

'Now, bear in mind exactly what Fley said when he suddenly flew in to confront Grimaud that night at the tavern. Study why he said and did certain things, and you will see that even shaky - minded Fley was very far from being as mad as he liked to pretend. Why, if he were intent merely on private vengeance, did he choose to confront Grimaud in the presence of a circle of friends and speak in just the innuendoes he used? He used his dead brother as a threat; and it was the only time he did speak of that dead brother. Why did he say, "He can be much more dangerous to you than I can"? Because the dead brother could hang Grimaud! Why did he say, "I don't want your life; he does"? Why did he say, "Shall I have him call on you?"? And then why, just afterwards, did he hand Grimaud his card on which his own address was carefully written? The giving of that card, combined with his words and later fictions, is significant. What Fley really meant, veiled so that he could throw a scare into Grimaud before witnesses, was just this; "You, my brother, are fat and rich on the proceeds of a robbery we both committed when we were young. I am poor - and I hate my work. Now will you come and call on me at my address, so that we can arrange this matter, or shall I set the police on you?"'

'Blackmail,' said Hadley, softly.

'Yes. Fley had a bee in his bonnet, but Fley was far from being a fool. Now mark how he twisted round his meaning in his last threatening words to Grimaud. "I also am in danger when I a.s.sociate with my brother, but I am prepared to run that risk." And in that case, as always afterwards, he was referring in strict truth to Grimaud. "You, my brother, might also kill me as you killed the other, but I will risk it. So shall I call on you amiably, or will my other dead brother come to hang you?"

'For think of his behaviour afterwards, on the night of his murder. Remember the glee he had of smashing up and getting rid of his illusion - properties? And what words did he use to O'Rourke? Words which, if you look at them squarely in the light of what we now know, can have only one explanation. He said: '"I shall not need them again. My work is finished. Didn't I tell you? I am going to see my brother. He will do something that will settle an old affair for both of us."

'Meaning, of course, that Grimaud had agreed to come to terms. Fley meant that he was leaving his old life for good; going back to his grave as a dead man with plenty of money; but he couldn't be more specific without blowing the gaff. Still, he knew that his brother was tricky; he'd had good reason in the past to know it. He couldn't leave behind him a big warning when he spoke with O'Rourke, in case Grimaud really meant to pay; but he threw out a hint: '"In case anything happens to me, you will find my brother in the same street where I myself live. That is not where he really resides, but he has a room there."

'I'll explain that last statement in just a moment. But go back to Grimaud. Now, Grimaud never had any intention of coming to terms with Fley. Fley was going to die. That wily, shrewd, theatrical mind of Grimaud's (who, as you know, was more interested in magical illusions than anybody else we have met) was determined not to suffer any nonsense from this inconvenient brother of his. Fley must die - but this was more difficult than it looked.

'If Fley had come to him in private, without anybody in the world ever being able to a.s.sociate Fley's name with his, it would have been simple. But Fley had been too shrewd for that. He had blazoned forth his own name and address, and hinted at mysterious secrets concerning Grimaud, before a group of Grimaud's friends. Awkward! Now if Fley is found obviously murdered, somebody is likely to say, "Hullo! Isn't that the chap who -?" And then presently there may be dangerous inquiries; because Lord knows what Fley may have told other people about Grimaud. The only thing he isn't likely to have confided to somebody else is his last deadly hold over Grimaud; and that is the thing about which he must be silenced. Whatever happens to Fley, however he dies, there are likely to be inquiries concerning Grimaud. The only thing to do is frankly to pretend that Fley is after his life; to send himself threatening letters (not too obviously); to stir up the household in an ingenious way; finally, to inform everybody that Fley has threatened to call on him on the night he himself intends to call on Fley. You will see very shortly just how he planned to work out a very brilliant murder.

'The effect he intended to produce was this: The murderous Fley should be seen calling on him on Sat.u.r.day night. There should be witnesses to this. The two should be together alone when Fley goes into his study. A row is heard, the sound of a fight, a shot, and a fall. The door being opened, Grimaud should be found alone - a nasty - looking but superficial wound from a bullet scratched along his side. No weapon is there. Out of the window hangs a rope belonging to Fley, by which Fley is a.s.sumed to have escaped. (Remember, it had been predicted that there would be no snow that night, so it would have been impossible to trace footprints.) Grimaud says: "He thought he killed me; I pretended to be dead; and he escaped. No, don't set the police on him, poor devil. I'm not hurt." And the next morning Fley would have been found dead in his own room. He would have been found, a suicide, having pressed his own gun against his chest and pulled the trigger. The gun is beside him. A suicide note lies on the table. In despair at thinking he has killed Grimaud, he has shot himself ... That, gentlemen, was the illusion Grimaud intended to produce.'

'But how did he do it?' demanded Hadley. 'And, anyway, it didn't turn out like that!'

'No. You see, the plan miscarried badly. The latter part of the illusion of Fley calling on him in his study when actually Fley would already have been dead in the Cagliostro Street house - I'll deal with in its proper place. Grimaud, with the aid of Madame Dumont, had already made certain preparations.

'He had told Fley to meet him at Fley's room on the top floor over the tobacconist's. He had told Fley to meet him there at nine o'clock on the Sat.u.r.day night, for a cash settlement. (You recall that Fley, gleefully throwing up his job and burning his properties, left the theatre in Limehouse at about eight - fifteen.) 'Grimaud had chosen Sat.u.r.day night because that night, by inviolable custom, he remained alone all evening in his study without anyone being allowed to disturb him for any reason whatsoever. He chose that night because he needed to use the areaway door, and go and come by way of the bas.e.m.e.nt; and Sat.u.r.day night was the night out for Annie, who had her quarters there. You'll remember that, after he went up to his study at seven - thirty, n.o.body did see him until, according to the evidence, he opened the study door to admit the visitor at nine - fifty. Madame Dumont claimed to have spoken to him in the study at nine - thirty, when she gathered up the coffee things. I'll tell you shortly why I disbelieved that statement - the fact is, he was not in the study at all: he was in Cagliostro Street. Madame Dumont had been told to lurk round the study door at nine - thirty, and to come out for some excuse. Why? Because Grimaud had ordered Mills to come upstairs at nine - thirty, you see, and watch the study door from the room down the hall. Mills was to be the dupe of the illusion Grimaud meant to work. But if - as he came upstairs near the study door - Mills had for any reason taken it into his head to try to speak with Grimaud, or see him, Dumont was there to head him off. Dumont was to wait in the archway, and keep Mills away from that door if he showed any curiosity.

'Mills was chosen as the dupe of the illusion: why? Because, although he was so meticulously conscientious that he would carry out his instructions to the tick, he was so afraid of "Fley" that he would not interfere when the hollow man came stalking up those stairs. It was not only that he must not attack the man in the false face in those dangerous few moments before the man got into the study (as, for instance, Mangan or even Drayman might have done), but also that he must not even venture out of his room. He had been told to stay in that room, and he would. Finally, he had been chosen because he was a very short man, a fact which will presently become clear.

'Now, he was told to go upstairs and watch at nine - thirty. This was because the hollow man was timed to make his appearance only a little afterwards; although, in fact, the hollow man was late. Mark one discrepancy. Mills was told nine - thirty - but Mangan was told ten o'clock! The reason is obvious. There was to be somebody downstairs to testify that a visitor had really arrived by the front door, confirming Dumont. But Mangan might be inclined towards curiosity about this visitor; he might be inclined to challenge the hollow man - unless he had first been jokingly told by Grimaud that the visitor would probably not arrive at all, or, if he did arrive, it could not possibly be before ten o'clock. All that was necessary was to throw his mind off, and make him hesitate long enough, for the hollow man to gel upstairs past that dangerous door. And, if the worst came to the worst, Mangan and Rosette could always be locked in.

'For everybody else: Annie was out. Drayman had been supplied with a ticket to a concert, Burnaby was unquestionably playing cards, and Pettis at the theatre. The field was clear.

'At some time before nine o'clock (probably about ten minutes) Grimaud slipped out of the house, using the area door up to the street. Trouble had already started. It had been snowing heavily for some time, contrary to rules. But Grimaud did not regard it as serious trouble. He believed he could do the business and return by half - past nine, and that it would still be snowing heavily enough to gla.s.s over any footprints that he would make or cause no comment on the absence of any footprints the visitor later should have made when the visitor would be supposed to have swung down from his window. In any case, his plans had been carried too far for him to back out.

'When he left the house he was carrying an old and untraceable Colt revolver, loaded with just two bullets. The sort of hat he wore I don't know, but his overcoat was a light yellow, glaring tweed with chicken - pox spots. He bought this coat several sizes too large. He bought it because it was the sort of coat he had never been known to wear and because n.o.body would recognize him in it if he were to be seen. He - '

Hadley intervened.

'Stop a bit! What about that business of the overcoats changing colour? That would come earlier in the evening. What had happened there?'

'Again I've got to ask you to wait until we get to the last illusion he worked; that's part of it.

'Well, Grimaud's purpose was to call on Fley. There he would speak with Fley amiably for a time. He would say something like: "You must leave this hovel, brother! You will be comfortably off now; I will see to that. Why not leave these useless possessions behind and come to my house? Let your landlord have the d.a.m.ned things in place of notice!" - Any sort of speech, you see, the purpose being to make Fley write one of his ambiguous notes for the landlord. "I am leaving for good." "I am going back to my grave." Anything that could be understood as a suicide note when Fley was found dead with a gun in his hand.'

Dr Fell leaned forward. 'And then Grimaud would take out his Colt, jam it against Fley's chest, and smilingly pull the trigger.

'It was the top floor of an empty house. As you have seen, the walls are astonishingly thick and solid. The landlord lived far down in the bas.e.m.e.nt, and was the most incurious man in Cagliostro Street. No shot, especially a m.u.f.fled shot with the gun held against Fley, could have been heard. It might be some time before the body was discovered; it would certainly not be before morning. And in the meantime, what will Grimaud do? After killing Fley he will turn the same gun on himself to give himself a slight wound, even if he has to imbed the bullet - he had, as we know from that little episode of the three coffins years before, the const.i.tution of an ox and the nerve of h.e.l.l. He would leave the gun beside Fley. He would quite coolly dap a handkerchief or cotton - wool across this wound, which must be inside the coat and across the shirt; bind it with adhesive tape until the time came to rip it open - and go back home to work his illusion, which should prove that Fley came to see him. That Fley shot him, and then returned to Cagliostro Street and used the same gun for suicide, no coroner's jury would afterwards doubt. Do I make it clear so far? It was crime turned the wrong way round.

'That, as I say, was what Grimaud intended to do. Had he performed it as he intended, it would have been an ingenious murder; and I doubt whether we should ever have questioned Fley's suicide.

'Now, there was only one difficulty about accomplishing this plan. If anybody - not anybody recognizable as himself, but anybody at all - were seen visiting Fley's house, the fat would be in the fire. It might not appear so easily as suicide. There was only one entrance from the street - the door beside the tobacconist's. And he was wearing a conspicuous coat, in which he had reconnoitred the ground beforre. (By the way, Dolberman, the tobacconist, had seen him hanging about previously.) He found the solution of his difficulty in Burnaby's secret flat.

'You see, of course, that Grimaud was the likeliest person of all to have known of Burnaby's flat in Cagliostro Street? Burnaby himself told us that, some months before, when Grimaud suspected him of having an ulterior motive in painting that picture, Grimaud had not only questioned him - he had watched him. From a man who was in such fancied danger, it would have been real watching. He knew of the flat. He knew from spying that Rosette had a key. And so, when the time came and the idea occurred to him, he stole Rosette's key.

'The house in which Burnaby had his flat was on the same side of the street as the house where Fley lived. All I hose houses are built side by side, with flat roofs; so that you have only to step over a low dividing wall to walk on the roofs from one end of the street to the other. Both men, remember, lived on the top floor. You recall what we saw when we went up to look at Burnaby's flat - just beside the door to the flat?'

Hadley nodded. 'Yes, of course. A short ladder going to a trap - door in the roof.'

'Exactly; And on the landing just outside Fley's room, there is a low skylight also communicating with the roof. Grimaud had only to go to Cagliostro Street by the back way, never appearing in the street itself, but going up the alley which we saw from Burnaby's window. He came in the back door (as we saw Burnaby and Rosette do later) he went up to the top floor and thence to the roof. Then he followed the roofs to Fley's lodgings, descended from the skylight to the landing, and could both enter and leave the place without a soul seeing him. Moreover, he knew absolutely that that night Burnaby would be playing cards elsewhere.

'And then everything went wrong.

'He must have got to Fley's lodgings before Fley arrived there himself; it wouldn't do to make Fley suspicious by being seen coming from the roof. But we know that Fley had some suspicions already. This may have been caused by Grimaud's request for Fley to bring along one of his long conjuring - ropes ... Grimaud wanted that rope as a piece of evidence to use later against Fley. Or it may have been caused by Fley's knowledge that Grimaud had been hanging about in Cagliostro Street for the past couple of days; possibly seeing him duck across the roofs towards Burnaby's after one reconnoitring, and thereby making Fley believe he had taken a room in the street.

'The two brothers met in that gas - lit room at nine. What they talked about we don't know. We shall never know. But evidently Grimaud lulled Fley's suspicions; they became pleasant and amiable and forgot old scores; Grimaud jocularly persuaded him to write that note for the landlord. Then - '

'I'm not disputing all this,' said Hadley, quietly,' but how do you happen to know it?'

'Grimaud told us,' said Dr Fell.

Hadley stared.

'Oh, yes. Once I had tumbled to that terrible mistake in times, I could understand. But to continue: 'Fley had written his note. He had got into his hat and coat for departure - because Grimaud wished it to be a.s.sumed that he had killed himself just after having returned from a journey outdoors: his return from the phantom visit to Grimaud, in other words. They were all ready to go. And then Grimaud leaped.

'Whether Fley was subconsciously on his guard; whether he twitched round to run for the door, since he was no match for the powerful Grimaud; whether it happened in. the twisting and scuffle - this we do not know. But Grimaud, with the gun against Fley's coat as Fley wrenched round from him, made a h.e.l.lish mistake. He fired. And he put the bullet in the wrong place. Instead of getting his victim through the heart, he got him under the left shoulder - blade: a wound of almost the same sort, although at the back, as the one from which Grimaud later died himself. It was a fatal wound, but far from instantly fatal. The poetic ironies were working to kill these brothers, with interchangeable methods, in precisely the same way.

'Of course Fley went down. He could do nothing else; and it was the wisest course, or Grimaud might have finished him. But Grimaud, for a second, must have lost his nerve in sheer terror. This might have wrecked his whole plan. Could a man shoot himself in that spot? If not. G.o.d help the murderer. And worse - Fley, not caught quickly enough, had screamed out before the bullet went home, and Grimaud thought he heard pursuers.

'He had sense enough, and guts enough, even in that h.e.l.lish moment, to keep his head. He jammed the pistol into the hand of the motionless Fley, lying on his face. He picked up the coil of rope. Somehow, in spite of crash and fuddlement, the plan must go on. But he had more sense than to risk the noise of another shot to be heard by people possibly listening, or to waste more time. He darted out of the room.

'The roof, do you see! The roof was his only chance. He heard imaginary pursuers everywhere; maybe some grisly recollection came back to him of three graves in a storm below the Hungarian mountains. He imagined that they would hear him and track him across those roofs. So he dashed for the trap - door at Burnaby's, and down into the dark of Burnaby's flat.

'It was only then that his wits began to recover themselves ...

'And, meantime, what has happened? Pierre Fley is fatally hurt. But he still has the ribs of that iron frame which once enabled him to survive being buried alive. The murderer has gone. And Fley will not give in. He must get help. He must get to - 'To a doctor, Hadley. You asked yesterday why Fley was walking towards the other end of the street, towards the end of a blind alley. Because (as you saw in the newspaper) a doctor lived there: the doctor to whose office he later was carried. He is mortally hurt and he knows it; but he will not be beaten! He gets up, still in his hat and overcoat. The gun has been put into his hand; he rams it in his pocket, for it may be useful. Down he goes, downstairs as steadily as he can, to a silent street where no alarm has been raised. He walks on -'

'Have you asked yourself why he was walking in the middle of the street and kept looking so sharply round? The most reasonable explanation is not that he was going to visit anybody; but that he knew the murderer to be lurking somewhere, and he expected another attack. He thinks he is safe. Ahead of him, two men are walking rapidly. He pa.s.ses a lighted jeweller's, he sees a street lamp ahead on the right - 'But what has happened to Grimaud? Grimaud has heard no pursuit, but he is half insane with wondering. He does not dare go back to the roof and risk investigation. But stop a moment! If there has been any discovery, he will be able to know by looking for a second out into the street. He can go down to the front door, look out, and peer up the street, can't he? No danger in that, since the house where Burnaby lives is deserted.

'He goes softly downstairs. He opens the door softly, having unb.u.t.toned his coat to wind the coil of rope round him inside that overcoat. He opens the door - full in the glow of a street lamp just beyond that door - and facing him, walking slowly in the middle of the street, is the man he left for dead in the other house less than ten minutes ago.

'And for the last time those brothers come face to face.

'Grimaud's shirt is a target under that street lamp. And Fley, driven mad with pain and hysteria, does not hesitate. He screams. He cries the words, "The second bullet is for you!" - just before he whips up the same pistol and fires.

'That effort is too much. The haemorrhage has got him, und he knows it. He screams again, lets go the gun as he tries to throw it (now empty) at Grimaud; and then he pitches forward on his face. That, my lads, is the shot which the three witnesses heard in Cagliostro Street. It was the shot which struck Grimaud in the chest just before he had time to close the door.'

CHAPTER 21.

THE UNRAVELLING.

'AND then?' prompted Hadley, as Dr Fell paused and lowered his head.

'The three witnesses did not see Grimaud, of course,' said Dr Fell, wheezing, after a long pause, 'because he was never outside the door; never on the steps at all; never within twenty feet of the man who seemed to have been murdered in the middle of a snow desert. Of course Fley already had the wound, which jetted blood from the last convulsion. Of course any deduction from the direction of the wound was useless. Of course there were no fingerprints on the gun, since it landed in snow and in a literal sense had been washed clean.'

'By G.o.d!' said Hadley, so quietly that he seemed to be making a statement. 'It fulfils every condition of the facts, and yet I never thought of it... But go on. Grimaud?'

'Grimaud is inside the door. He knows he's got it in his chest; but he doesn't think it's very serious. He's survived worse things than bullets, and other things (he thinks) are more serious.

'After all, he's only got what he was going to give himself - a wound. He could bark out that chuckle of his at such a thing. But his plan has crashed to h.e.l.l! (How is he to know, by the way, that the clock at the jeweller's will be fast? He doesn't even know that Fley is dead, for there is Fley walking in the street with fire and sting still in him. Luck - by reason of the jeweller's clock - is with him when he thought it had deserted him, but how is he to know it?) All he is sure of is that Fley will never now be found, a suicide up in that little room. Fley - probably dangerously wounded, yes, but still able to talk - is out in that street with a policeman running towards him. Grimaud is undone. Unless he can use his wits, he's on his way to the hangman, for Fley will not keep silent now.

'All this comes an instant after the shot, the rush of fancies crowding in. He can't stay here in this dark hall. He'd better have a look at that wound, though, and make sure he doesn't leave a trail of blood. Where? Burnaby's flat upstairs, of course. Up he goes, gets the door open, and switches on the lights. Here's the rope wound round him - no use for that thing now; he can't pretend Fley came to call on him when Fley may now be talking with the police. He flings the rope off and leaves it.

'A look at the wound next. There's blood all over the inside of that light tweed overcoat, and blood on his inner clothes. But the wound is of small consequence. He's got his handkerchief and his adhesive tape, and he can plug himself up like a horse gored in the bull ring. Karoly Horvath, whom nothing can kill, can afford to chuckle at this. He feels as steady and fresh as ever. But he patches himself up - hence the blood in the bathroom of Burnaby's flat - and tries to collect his wits. What time is it? Good G.o.d! he's late; it's just on a quarter to ten. Got to get out of here and hurry home before they catch him...

'And he leaves the lights on. When they burnt up a shilling's worth and went out in the later course of the night, we don't know. They were on three - quarters of an hour afterwards, anyhow, when Rosette saw them.

'But I think that his sanity returns as he hurries home. Is he caught? It seems inevitable. Yet is there any loophole, any ghost of a fighting chance, however thin? You see, whatever else Grimaud is, he's a fighter. He's a shrewd, theatrical, imaginative, sneering, common - sense blackguard: but don't forget that he's also a fighter. He wasn't all of a black colour, you know. He would murder a brother, but I question whether he would murder a friend or a woman who loved him. In any case, is there some way out? There's one chance, so thin that it's almost useless; but the only one. That's to carry through his original scheme and pretend that Fley has called on him and given that wound in his own house. Fley still has the gun. It will be Grimaud's story, and his witnesses' word, that he never left the house all the evening! Whereas they can swear that Fley did come to see him - and then let the d.a.m.ned police try to prove anything! Why not? The snow? It's stopped snowing and Fley won't have left a track. Grimaud has thrown away the rope Fley was supposed to have used. But it's a toss - up, a last daring of the devil, the only course in an extremity...

'Fley shot him at about twenty minutes to ten. He gets back here at a quarter to ten or a little after. Getting into the house without leaving a footprint? Easy! for a man with a const.i.tution like an ox, and only slightly wounded. (By the way, I believe he was really wounded only slightly, and that he'd live now to hang, if he hadn't done certain things; you'll see.) He'll return by way of the steps down to the area - way, and the area door, as arranged. How? Well, there is a coating of snow on the areaway steps, of course. But the entrance to the areaway steps is beside the next house, isn't it? Yes. And at the foot of the area steps the bas.e.m.e.nt door is protected from snow by a projection: the projection of the main front steps overhanging. So that there is no snow exactly in front of the area door. If he can get down there without leaving a mark - 'He can. He can approach from the other direction, as though he were going to the house next door, and then simply jump down the area steps to the cleared patch below ... Don't I seem to remember a thud, as of someone falling, which someone heard just before the front - door bell rang?'

'But he didn't ring the front - door bell!'

'Oh, yes, he did - but from inside. After he'd gone into the house by way of the area door, and up to where Ernestine Dumont was waiting for him. Then they were ready to perform their illusion.'

'Yes,' said Hadley. 'Now we come to the illusion. How was it done, and how do you know how it was done?'

Dr Fell sat back and tapped his finger - tips together as though he were marshalling facts.

'How do I know? Well, I think my first suggestion was the weight of that picture.' He pointed sleepily at the big slashed canvas leaning against the wall. 'Yes, it was the weight of the picture. That wasn't very helpful, until I remembered something else...'

'Weight of the picture? Yes, the picture,' growled Hadley. 'I'd forgotten that. How does it figure in the blasted business, anyhow? What did Grimaud mean to do with that?'

'H'mf, ha, yes. That's what I wondered, you see.'

'But the weight of the picture, man! It doesn't weigh very much. You yourself picked it up with one hand and turned it round in the air.'

Dr Fell sat up with an air of some excitement. ' Exactly. You've hit it. I picked it up with one hand and swung it round ... Then why should it take two husky men, the cabman and one extra, to carry it upstairs?'

'What?'

'It did, you know. That was twice pointed out to us. Grimaud, when he took it from Burnaby's studio, easily carried it downstairs. Yet, when he returned here with that same painting late in the afternoon, two people had a job carting it up. Where had it picked up so much weight all of a sudden? He didn't have gla.s.s put in it - you can see that for yourself. Where was Grimaud all that time, between the morning when he bought the picture and the afternoon when he returned with it? It's much too big a thing to carry about with you for pleasure. Why was Grimaud so insistent on having the picture all wrapped up?

'It wasn't a very far - fetched deduction to think that he used that picture as a blind to hide something that the men were carrying up, unintentionally, along with it. Something in the same parcel. Something very big - seven feet by four - h'm -'

'But there couldn't have been anything,' objected Hadley, 'or we'd have found it in this room, wouldn't we? Besides, in any case the thing must have been almost absolutely flat, or it would have been noticed in the wrappings of the picture. What sort of object is it that's as big as seven feet by four, and yet thin enough not to be noticed inside the wrappings of a picture; what's as huge an object as that picture, which can nevertheless be spirited out of sight whenever you wish?'

'A mirror,' said Dr Fell.

After a sort of thunderous silence, while Hadley rose from his chair, Dr Fell went on sleepily: 'And it can be spirited out of sight, as you put it, merely by being pushed up the flue of that very broad chimney - where we've all tried to get our fists, by the way - and propped up on the ledge inside where the chimney turns. You don't need magic. You only need to be d.a.m.nably strong in the arms and shoulders.'

'You mean,' cried Hadley,' that d.a.m.ned stage trick - '

'A new version of the stage trick,' said Dr Fell, 'and a very good one which is practical if you care to try it. Now, look round this room. You see the door? What do you see in the wall directly opposite the door?'

'Nothing,' said Hadley. 'I mean, he's had the bookcases cleared away in a big s.p.a.ce on either side. There's blank panelled wall, that's all.'

'Exactly. And do you see any furniture in a line between the door and that wall?'

'No. It's cleared.'

'So, if you were out in that hall looking in, you would see only black carpet, no furniture, and to the rear an expanse of blank oak - panelled wall?'

'Yes.'

'Now, Ted, open the door and look out into the hall,' said Dr Fell. 'What about the walls and carpet out there?'

Rampole made a feint of looking, although he knew. 'They're just the same,' he said. 'The floor is one solid carpet running to the baseboards, like this one, and the panelling is the same.'

'Right! By the way, Hadley,' pursued Dr Fell, still drowsily, 'you might drag out that mirror from behind the bookcase over there. It's been behind the bookcase since yesterday afternoon, when Drayman found it in the chimney. It was lifting it down that brought on his stroke. We'll try a little experiment. I don't think any of the household will interrupt us up here, but we can head off anybody who does. I want you to take that mirror, Hadley, and set it up just inside the door - so that when you open the door (it opens inwards and to the right, you see, as you come in from the hall) the edge of the door at its outermost swing is a few inches away from the mirror.'

The superintendent, with some difficulty, trundled out the object he found behind the bookcase. It was bigger than a tailor's swinging mirror; several inches, in fact, higher and wider than the door. Its base rested flat on the carpet, and it was supported upright by a heavy swing - base on the right - hand side as you faced it. Hadley regarded it curiously.

'Set it up inside the door?'

'Yes. The door will swing open a short distance; you'll see an aperture only a couple of feet wide at the most ... Try it!'

'I know, but if you do that - well, somebody sitting in the room down at the end of the hall, where Mills was, would see his own reflexion smack in the middle of the mirror.'

'Not at all. Not at the angle - a slight angle, but enough; a poor thing, but mine own - not at the angle to which I'm going to tilt it. You'll see. The two of you go down there where Mills was while I adjust it. Keep your eyes off until I sing out.'

Hadley, muttering that it was d.a.m.ned foolishness, but highly interested in spite of that, tramped down after Rampole. They kept their eyes off until they heard the doctor's hail, and then turned round.

The hallway was gloomy and high enough. Its black - carpeted length ran down to a closed door. Dr Fell stood outside that door, like an overfat master of ceremonies about to uuveil a statue. He stood a little to the right of the door, well back from it against the wall, and had his hand stretched out across to the k.n.o.b.

'Here she goes!' he grunted, and quickly opened the door - hesitated - and closed it. 'Well? What did you see?'

'I saw the room inside,' returned Hadley. 'Or at least I thought I did. I saw the carpet, and the rear wall. It seemed a very big room.'