'You didn't see that,' said Dr Fell. 'As a matter of fact, you saw the reflexion of the panelled wall immediately to the right of the door where you're standing, and the carpet going up to it. That's why it seemed so big a room: you were looking at a double length of reflexion. This mirror is bigger than the door, you know. And you didn't see a reflexion of the door itself because it opens inwards to the right. If you looked carefully, you might have seen a line of what looks like shadow just along the top edge of the door. That's where the top edge of the mirror inevitably reflects, being taller, an inch or so of the inner top edge of the door. But your attention would be concentrated on any figures you saw ... Did you see me, by the way?'

'No; you were too far over. You had your arm across the door to the k.n.o.b, and kept back.'

'Yes. As Dumont was standing. Now try a last experiment before I explain how the whole mechanism worked. Ted, you sit down in the chair behind that desk - where Mills was sitting. You're very much taller than he is, but it will ill.u.s.trate the idea. I'm going to stand outside, with this door open, and look at myself in the mirror. Now, you can't mistake ME, either from the front or the rear; but then I'm more distinguishable than some people. Just tell me what you see.'

In the ghostly light, with the door partly open, the effect was rather eerie. A figure of Dr Fell stood inside the door, peering out at another figure of Dr Fell standing on the threshold and confronting himself - fixed and motionless, with a startled look.

'I don't touch the door, you see,' a voice boomed at them. By the illusion of the moving lips Rampole would have sworn that the Dr Fell inside the door was speaking. The mirror threw the voice back like a sounding - board. 'Somebody obligingly opens and closes the door for me - some body standing at my right. I don't touch the door, or my reflexion would have to do likewise. Quick, what do you notice?'

'Why, one of you is very much taller,' said Rampole, studying the images.

'Which one?'

'You yourself; the figure in the hall.'

'Exactly. First because you're seeing it at a distance, but the most important thing is that you're sitting down. To a man the size of Mills I should look like a giant. Hey? H'mf. Hah. Yes. Now if I make a quick move to dodge in at that door (supposing me to be capable of such a manoeuvre), and at the same time my confederate at the right makes a quick confusing move with me and slams the door, in the muddled illusion the figure inside seems to be -?'

'Jumping in front of you to keep you out.'

'Yes. Now come and read the evidence, if Hadley has it.'

When they were again in the room, past the tilted mirror which Hadley moved back, Dr Fell sank into a chair, sighing wheezily.

'I'm sorry, gents. I should have realized the truth long before, from the careful, methodical, exact Mr Mills's evidence. Let me see if I can repeat from memory his exact words. Check me up, Hadley. H'm.' He rapped his knuckles against his head and scowled. 'Like this: '"She [Dumont] was about to knock at the door when I was startled to see the tall man come upstairs directly after her. She turned round and saw him. She exclaimed certain words ... The tall man made no reply. He walked to the door, and without haste turned down the collar of his coat and removed his cap, which he placed in his overcoat pocket..."

'You see, gents? He had to do that, because the reflexion couldn't show a cap and couldn't show a collar turned up when the figure inside must appear to be wearing a dressing - gown. But I wondered why he was so methodical about that, since apparently he didn't remove the mask - '

'Yes, what about that mask? Mills says he didn't - '

'Mills didn't see him take it off; I'll show you why as soon as we go on with Mills: '"Madame Dumont cried out something, shrank back against the wall, and hurried to open the door. Dr Grimaud appeared on the threshold -"

'Appeared! That's precisely what he did do. Our methodical witness is uncomfortably exact. But Dumont? There was the first flaw. A frightened woman, looking up at a terrifying figure while she's standing before the door of a room in which there's a man who will protect her, doesn't shrink back. She rushes towards the door to get protection. Anyhow, follow Mills's testimony. He says Grimaud was not wearing his eye - gla.s.ses (they wouldn't have fitted behind that mask). But the natural movement of a man inside, I thought, would have been to raise his gla.s.ses. Grimaud - according to Mills - stands stock - still the whole time; like the stranger, with his hands in his pockets. Now for the d.a.m.ning part. Mills says: "I am under the impression that Madame Dumont, although she was shrinking back against the wall, closed the door after him. I recall that she had her hand on the k.n.o.b." Not a natural action for her either! She contradicted him - but Mills was right.'

Dr Fell gestured. 'No use going on with all this. But here was my difficulty: if Grimaud was alone in that room, if he simply walked in on his own reflexion, what became of his clothes? What about that long black overcoat, the brown peaked cap, even the false face? They weren't in the room. Then I remembered that Ernestine Dumont's profession had been the making of costumes for the opera and ballet; I remembered a story O'Rourke had told us; and I knew - '

'Well?'

'That Grimaud had burnt them,' said Dr Fell. 'He had burnt them because they were made of paper, like the uniform of the Vanishing Horseman described by O'Rourke. He couldn't risk the long and dangerous business of burning real clothes in that fire; he had to work too fast. They had to be torn up and burnt. And bundles of loose, blank sheets of writing - paper - perfectly blank! - had to be burned on top of them to hide the fact that some of it was coloured paper. Dangerous letters! Oh, Bacchus, I could murder myself for thinking such a thing!' He shook his fist. 'When there was no blood - trail, no blood - stain at all, going to the drawer in his desk where he did keep his important papers! And there was another reason for burning papers - they had to conceal the fragments of the "shot".'

'Shot?'

'Don't forget that a pistol was supposed to have been fired in that room. Of course what the witnesses really heard was the noise of a heavy fire - cracker - pinched from the h.o.a.rd Drayman always keeps, as you know, for Guy Fawkes' night. Drayman discovered the missing thunderbolt; I think that's how he tumbled to the scheme, and why he kept muttering about "fireworks". Well, the fragments of an exploding fire - cracker fly wide. They're heavy reinforced cardboard, hard to burn, and they had to be destroyed in the fire or hidden in that drift of papers. I found some of them. Of course, we should have realized no bullet had really been fired. Modern cartridges - such as you informed me were used in that Colt revolver - have smokeless powder. You can smell it, but you can't see it. And yet there was a haze in this room (left by the fire - cracker) even after the window was up.

'Ah, well, let's recapitulate! Grimaud's heavy crepe - paper uniform consisted of a black coat - black like a dressing - gown, long like a dressing - gown, and having at the front shiny lapels which would show like a dressing - gown when you turned down the collar to face your own image. It consisted of a paper cap, to which the false face was attached - so that in sweeping off the cap you simply folded both together and shoved 'em into your pocket. (The real dressing - gown, by the way, was already in this room while Grimaud was out.) And the black "uniform", early last evening, had been incautiously hung up in the closet downstairs.

'Mangan, unfortunately, spotted it. The watchful Dumont knew that he spotted it, and whisked it out of that cupboard to a safer place as soon as he went away. She, naturally, never saw a yellow tweed coat hanging there at all. Grimaud had the tweed coat upstairs here with him, ready for his expedition. But it was found in the closet yesterday afternoon, and she had to pretend it had been there all the time. Hence the chameleon overcoat.

'You can now make a reconstruction of just what happened when Grimaud, after killing Fley and getting a bullet himself, returned to the house on Sat.u.r.day night. Right at the start of the illusion he and his confederate were in dangerous trouble. You see, Grimaud was late. He'd expected to be back by nine - thirty - and he didn't get there until a quarter to ten. The longer he delayed, the nearer it got to the time he had told Mangan to expect a visitor, and now Mangan would be expecting the visitor he had been told to watch. It was touch - and - go, and I rather imagine the cool Grimaud was fairly close to insane. He got up through the bas.e.m.e.nt entrance, where his confederate was waiting. The tweed coat, with the blood inside it, went into the hall closet to be disposed of presently - and it never was, because he died. Dumont eased open the door, rang the bell by putting her hand out, and then went to "answer" it while Grimaud was getting ready with his uniform.

'But they delayed too long. Mangan called out. Grimaud, with his wits still not functioning well, grew a little panicky and made a blunder to ward off immediate detection. He's got so far; he didn't want to fail then from the nosiness of a d.a.m.ned penniless kid. So he said that he was Pettis, and locked them in. (You notice that Pettis is the only one with a voice of the same ba.s.s quality as Grimaud's?) Yes, it was a spur - of - the - moment error, but his only wish was to writhe like a footballer down a field and somehow escape those hands for the moment.

'The illusion was performed; he was alone in his room. His jacket, probably with blood on that, had been taken in charge by Dumont; he wore the uniform over his shirt - sleeves, open shirt, and bandaged wound. He had only to lock the door behind him, put on his real dressing - gown, destroy the paper uniform, and get that mirror up into the chimney...

'That, I say again, was the finish. The blood had begun to flow again, you see. No ordinary man, wounded, could have stood the strain under which he had already been. He wasn't killed by Fley's bullet. He ripped his own lung like a rotted piece of rubber when he tried to - and super - humanly did - lift that mirror into its hiding - place. That was when he knew. Then was when he began to bleed from the mouth like a slashed artery; when he staggered against the couch, knocked away the chair, and reeled forward in his last successful effort to ignite the fire - cracker. After all the hates and dodgings and plans, the world was not spinning in front of him: it was only slowly going black. He tried to scream out, and he could not, for the blood was welling in his throat. And at that moment Charles Grimaud suddenly knew what he would never have believed possible, the breaking of the last and most shattering mirror - illusion in his bitter life ...'

'Well?'

'He knew that he was dying,' said Dr Fell. 'And, stranger than any of his dreams, he was glad.'

The heavy leaden light had begun to darken again with snow. Dr Fell's voice sounded weirdly in the chill room. Then they saw that the door was opening and that in it stood the figure of a woman with a d.a.m.ned face. A d.a.m.ned face and a black dress, but round her shoulders was still drawn a red and yellow shawl for love of the dead.

'You see, he confessed,' Dr Fell said in the same low, monotonous tone, 'he tried to tell us the truth about his killing of Fley, and Fley's killing of him. Only we did not choose to understand, and I didn't understand until I knew from the clock what must have happened in Cagliostro Street. Man, man, don't you see? Take first his final statement, the statement made just before he died: '"It was my brother who did it. I never thought he would shoot. G.o.d knows how he got out of that room - "'

'You mean Fley's room in Cagliostro Street, after Fley had been left for dead?' demanded Hadley.

'Yes. And the horrible shock of coming on him suddenly, as Grimaud opened the door under the street light. You see: '"One second he was there, and the next he wasn't... I want to tell you who my brother is, so you won't think I'm raving..."

'For of course he did not think anybody knew about Fley. Now, in the light of that, examine the tangled, muddled, half - choked words with which - when he heard the statement that he was sinking - he tried to explain the whole puzzle to us.

'First he tried to tell us about the Horvaths and the salt - mine. But he went on to the killing of Fley, and what Fley had done to him. "Not suicide." When he'd seen Fley in the street, he couldn't make Fley's death the suicide he pretended. "He couldn't use rope." Fley couldn't after that be supposed to use the rope that Grimaud had discarded as useless. "Roof." Grimaud did not mean this roof; but the other roof which he crossed when he left Fley's room. "Snow." The snow had stopped and wrecked his plans. "Too much light." There's the crux, Hadley! When he looked out into the street, there was too much light from the street lamp; Fley recognized him, and fired. "Got gun." Naturally, Fley had got the gun then. "Fox." The mask, the Guy Fawkes charade he tried to work. But finally, "Don't blame poor -" Not Drayman; he didn't mean Drayman. But it was a last apology for the one thing, I think, of which he was ashamed; the one piece of imposture he would never have done. "Don't blame poor Pettis; I didn't mean to implicate him,'"

For a long time n.o.body spoke.

'Yes,' Hadley agreed dully. 'Yes. All except one thing. What about the slashing of that picture, and where did the knife go?'

'The slashing of the picture, I think, was an extra touch of the picturesque to help the illusion; Grimaud did it - or so I imagine. As for the knife, I frankly don't know. Grimaud probably had it here, and put it up the chimney beside the mirror so that the invisible man should seem to be doubly armed. But it isn't on the chimney ledge now. I should suppose that Drayman found it yesterday, and took it away - '

'That is the one point,' said a voice, 'on which you are wrong.'

Ernestine Dumont remained in the doorway, her hands folded across the shawl at her breast. But she was smiling.

'I have heard everything you said,' she went on. 'Perhaps you can hang me, or perhaps not. That is not important. I do know that after so many years it is not quite worth while going on without Charles ... I took the knife, my friend. I had another use for it.'

She was still smiling, and there was a blaze of pride in her eyes. Rampole saw what her hands were hiding. He saw her totter suddenly, but he was too late to catch her when she pitched forward on her face. Dr Fell lumbered out of his chair and remained staring at her with a face as white as her own.

'I have committed another crime, Hadley,' he said. 'I have guessed the truth again.'